At Least $2021$ Terms

★ 6/10combinatorics algebra Binomial Theorem Polynomials

Problem

For a positive integer $n$ , the expansion of

(xy - 5x + 3y - 15)^n,

after combining like terms in $x^i y^j$ ( $i, j = 0, 1, \dots, n$ ), has at least $2021$ terms. Find the minimum value of $n$ .

Answer

Solution

Difficulty	6/10
Topics	combinatorics, algebra, Binomial Theorem, Polynomials

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