Euler's Pentagonal Numbers Theorem/Corollary 1/Examples/12

Example of Sigma of Integer equals Sum of Sequence of Sigma of Integers indexed by Generalized Pentagonal Numbers

 * $\sigma \left({12}\right) = \sigma \left({11}\right) + \sigma \left({10}\right) - \sigma \left({7}\right) - \sigma \left({5}\right) + 12$