MathCastle
ChallengeSuperchallenge

Challenge · Superchallenge problem

Compute ∑k≡2(mod5)(30k)\displaystyle\sum_{k \equiv 2 \pmod{5}} \binom{30}{k}, the sum of (30k)\binom{30}{k} over all kk from 00 to 3030 with k≡2(mod5)k \equiv 2 \pmod{5}.

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