PutnamSuperchallengeIntegrals I: Feynman's Trick ShareIntegrals I: Feynman's Trick · Superchallenge problemFind the coefficient of x20x^{20}x20 in (1+x+x2+⋯+x9)3\left(1 + x + x^2 + \cdots + x^9\right)^3(1+x+x2+⋯+x9)3.Check Show answer Walk through it step by step Practice more like this Review this concept