PutnamSuperchallengeIntegrals I: Feynman's Trick ShareIntegrals I: Feynman's Trick · Superchallenge problemEvaluate ∑n=1∞n3n\displaystyle\sum_{n=1}^\infty \frac{n}{3^n}n=1∑∞3nn.Check Show answer Walk through it step by step Practice more like this Review this concept