Alexander Molnar 14a89d5a56 Added content to stub (#34168) ... Explained what an arithmetic series is, gave the formula for the sum (when finite) and gave two proofs (not just induction) as the 'famous' method by Gauss is too elegant to ignore.		2018-11-02 22:09:56 +05:30
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index.md	Added content to stub (#34168)	2018-11-02 22:09:56 +05:30