If you're looking for value ideas, the following list might offer a good starting point for your own analysis.

Here we present 21 companies that have recently announced stock buybacks. These companies are also undervalued when comparing current price to the fair value price, calculated by the Graham Number equation.

Benjamin Graham, the man who developed this equation, was a former mentor of Warren Buffett and is the so-called godfather of value investing.

The Graham Number, or the maximum price an investor should pay for a stock, is derived using only two data points: Current earnings per share and current book value per share.

The Graham Number = Fair Value of a Stock = Square Root of (22.5) x (Earnings per Share) x (Book Value per Share).

The math of the Graham number is relatively straightforward. It is predicated on the belief that the price-to-earnings (P/EPS) ratio should be no more than 15, and the price-to-book value (P/BVPS) ratio should be no more than 1.5. Therefore we only include companies that meet both of these criteria.

From the criteria, the product of the two should not be more than 22.5. In other words, (P/EPS of 15) x (P/BVPS of 1.5) = 22.5, from which the equation was created.

When companies buy back their own stock, they use excess cash to reduce the number of shares outstanding, which directly increases earnings per share and (at least theoretically) adds value for shareholders. Some might even argue that management teams use buybacks to signal that their stock is undervalued.

Do you think these companies are undervalued? Full details below.

Graham input data sourced from Yahoo! Finance, all other data sourced from Finviz.

*Click for expanded images*

List sorted by implied potential upside.**1. White River Capital Inc (NYSEMKT:RVR):** Credit Services Industry. Market cap of $64.55M. The company announced a stock buyback of $0.5M on 11/02/10. BVPS at $22.40, diluted EPS at $1.84. Graham number = sqrt(22.5 x $22.40 x $1.84) = $30.45. Current price at $17.54 (implies a potential upside of 73.62%). RVR has a relatively low correlation to the market (beta = 0.38), which may be appealing to risk-averse investors. The stock has gained 45.24% over the last year. **2. Validus Holdings, Ltd. (NYSE:VR)**: Property and Casualty Insurance Industry. Market cap of $2.96B. The company announced a stock buyback of $400M on 12/20/10. BVPS at $35.76, diluted EPS at $3.34. Graham number = sqrt(22.5 x $35.76 x $3.34) = $51.84. Current price at $30.00 (implies a potential upside of 72.80%). The stock has gained 19.99% over the last year. **3. Fidelity National Financial, Inc. (NYSE:FNF): **Surety and Title Insurance Industry. Market cap of $3.07B. The company announced a stock buyback of $5M on 01/27/11. BVPS at $15.50, diluted EPS at $1.61. Graham number = sqrt(22.5 x $15.50 x $1.61) = $23.70. Current price at $13.75 (implies a potential upside of 72.33%).**4. Hallmark Financial Services Inc. (NASDAQ:HALL):** Property and Casualty Insurance Industry. Market cap of $178.26M. The company announced a stock buyback of $3M on 01/24/11. BVPS at $11.71, diluted EPS at $0.81. Graham number = sqrt(22.5 x $11.71 x $0.81) = $14.61. Current price at $8.72 (implies a potential upside of 67.53%). PEG ratio at 0.73, and P/FCF ratio at 4.1. The stock has gained 9.11% over the last year. **5. Unitrin Inc. (UTR)**: Property and Casualty Insurance Industry. Market cap of $1.78B. The company announced a stock buyback of $300M on 02/02/11. BVPS at $34.61, diluted EPS at $2.98. Graham number = sqrt(22.5 x $34.61 x $2.98) = $48.17. Current price at $28.90 (implies a potential upside of 66.69%). The stock has gained 9.2% over the last year. **6. XL Group plc (NYSE:XL):** Property and Casualty Insurance Industry. Market cap of $7.18B. The company announced a stock buyback of $1.0B on 11/02/10. BVPS at $33.54, diluted EPS at $1.73. Graham number = sqrt(22.5 x $33.54 x $1.73) = $36.13. Current price at $22.08 (implies a potential upside of 63.64%). The stock has gained 18.41% over the last year. **7. Unum Group (NYSE:UNM)**: Accident and Health Insurance Industry. Market cap of $7.96B. The company announced a stock buyback of $1.0B on 02/02/11. BVPS at $28.25, diluted EPS at $2.71. Graham number = sqrt(22.5 x $28.25 x $2.71) = $41.50. Current price at $25.48 (implies a potential upside of 62.89%). PEG ratio at 0.77, and P/FCF ratio at 7.36. The stock has gained 7.62% over the last year. **8. ProAssurance Corporation (NYSE:PRA):** Property and Casualty Insurance Industry. Market cap of $1.87B. The company announced a stock buyback of $200M on 11/11/10. BVPS at $60.35, diluted EPS at $7.20. Graham number = sqrt(22.5 x $60.35 x $7.20) = $98.88. Current price at $61.48 (implies a potential upside of 60.83%). PEG ratio at 0.82, and P/FCF ratio at 13.47. The stock has gained 5.22% over the last year. **9. The Travelers Companies, Inc. (NYSE:TRV):** Property and Casualty Insurance Industry. Market cap of $25.23B. The company announced a stock buyback of $5.0B on 01/25/11. BVPS at $58.46, diluted EPS at $6.62. Graham number = sqrt(22.5 x $58.46 x $6.62) = $93.31. Current price at $58.49 (implies a potential upside of 59.54%). The stock has gained 13.81% over the last year. **10. The Chubb Corporation (NYSE:CB)**: Property and Casualty Insurance Industry. Market cap of $17.22B. The company announced a stock buyback of $30M on 12/09/10. BVPS at $52.24, diluted EPS at $6.76. Graham number = sqrt(22.5 x $52.24 x $6.76) = $89.14. Current price at $58.22 (implies a potential upside of 53.11%). CB has a relatively low correlation to the market (beta = 0.49), which may be appealing to risk-averse investors. The stock may be undervalued at current levels, with a PEG ratio at 0.9, and P/FCF ratio at 9.43. The stock has gained 18.89% over the last year. **11. Material Sciences Corp. (NASDAQ:MASC):** Industrial Equipment and Components Industry. Market cap of $79.91M. The company announced a stock buyback of $1.0M on 01/28/11. BVPS at $5.82, diluted EPS at $0.59. Graham number = sqrt(22.5 x $5.82 x $0.59) = $8.79. Current price at $6.23 (implies a potential upside of 41.09%). Note that this is a risky stock that is significantly more volatile than the overall market (beta = 2.21). The stock has performed poorly over the last month, losing 10.81%. **12. Aetna Inc. (NYSE:AET)**: Health Care Plans Industry. Market cap of $13.83B. The company announced a stock buyback of $750M on 12/03/10. BVPS at $25.73, diluted EPS at $4.18. Graham number = sqrt(22.5 x $25.73 x $4.18) = $49.19. Current price at $35.38 (implies a potential upside of 39.04%). PEG ratio at 0.79, and P/FCF ratio at 12.31. The stock has gained 12.75% over the last year. **13. W.R. Berkley Corporation (NYSE:WRB):** Property and Casualty Insurance Industry. Market cap of $4.21B. The company announced a stock buyback of $10M on 11/03/10. BVPS at $26.26, diluted EPS at $2.90. Graham number = sqrt(22.5 x $26.26 x $2.90) = $41.39. Current price at $30.15 (implies a potential upside of 37.29%). The stock is a short squeeze candidate, with a short float at 7.28% (equivalent to 10.83 days of average volume). The stock has gained 17.04% over the last year. **14. Nasdaq OMX Group Inc. (NASDAQ:NDAQ):** Diversified Investments Industry. Market cap of $4.55B. The company announced a stock buyback of $22.78M on 12/16/10. BVPS at $26.84, diluted EPS at $1.91. Graham number = sqrt(22.5 x $26.84 x $1.91) = $33.96. Current price at $25.28 (implies a potential upside of 34.35%). The stock has gained 27.51% over the last year. **15. Education Management Corporation (NASDAQ:EDMC):** Education and Training Services Industry. Market cap of $1.43B. The company announced a stock buyback of $100M on 12/08/10. BVPS at $15.60, diluted EPS at $1.78. Graham number = sqrt(22.5 x $15.60 x $1.78) = $25.00. Current price at $19.19 (implies a potential upside of 30.25%). PEG ratio at 0.71, and P/FCF ratio at 6.95. Short float at 6.84% (equivalent to 17.92 days of average volume), implying EDMC is a short squeeze candidate. The stock has lost 18.62% over the last year. **16. The Dolan Company (NYSE:DM): **Publishing Industry. Market cap of $360.02M. The company announced a stock buyback of $2.0M on 12/07/10. BVPS at $9.24, diluted EPS at $1.07. Graham number = sqrt(22.5 x $9.24 x $1.07) = $14.91. Current price at $11.68 (implies a potential upside of 27.70%). PEG ratio at 0.63, and P/FCF ratio at 6.51. The stock has performed poorly over the last month, losing 15.23%. **17. JAKKS Pacific, Inc. (NASDAQ:JAKK): **Toys and Games Industry. Market cap of $490.23M. The company announced a stock buyback of $30M on 10/26/10. BVPS at $15.28, diluted EPS at $1.52. Graham number = sqrt(22.5 x $15.28 x $1.52) = $22.86. Current price at $18.02 (implies a potential upside of 26.86%). The stock is a short squeeze candidate, with a short float at 14.68% (equivalent to 22.45 days of average volume). It's been a rough couple of days for the stock, losing 5.32% over the last week. **18. Entergy Corporation (NYSE:ETR):** Electric Utilities Industry. Market cap of $12.26B. The company announced a stock buyback of $500M on 10/29/10. BVPS at $47.53, diluted EPS at $6.66. Graham number = sqrt(22.5 x $47.53 x $6.66) = $84.39. Current price at $67.76 (implies a potential upside of 24.55%). ETR has lost 6.56% over the last week. **19. Markel Corp. (NYSE:MKL)**: Property and Casualty Insurance Industry. Market cap of $3.84B. The company announced a stock buyback of $200M on 12/01/10. BVPS at $326.36, diluted EPS at $27.27. Graham number = sqrt(22.5 x $326.36 x $27.27) = $447.49. Current price at $393.44 (implies a potential upside of 13.74%). The stock has gained 5.87% over the last year. **20. Ameron International Corporation (NYSE:AMN-OLD):** General Building Materials Industry. Market cap of $663.50M. The company announced a stock buyback of $50M on 10/22/10. BVPS at $55.18, diluted EPS at $5.00. Graham number = sqrt(22.5 x $55.18 x $5.00) = $78.79. Current price at $71.79 (implies a potential upside of 9.75%). The stock has gained 9.61% over the last year. **21. Cytec Industries Inc. (NYSE:CYT): **Specialty Chemicals Industry. Market cap of $2.57B. The company announced a stock buyback of $150M on 01/27/11. BVPS at $35.00, diluted EPS at $3.46. Graham number = sqrt(22.5 x $35.00 x $3.46) = $52.20. Current price at $51.52 (implies a potential upside of 1.32%). The stock has gained 15.86% over the last year.**Disclosure: **I have no positions in any stocks mentioned, and no plans to initiate any positions within the next 72 hours.