If the binomial coefficients of the second, third and fourth terms in the expansion of (1 + x) ^ n are known to be an arithmetic sequence, then n can be obtained

2,3,4, the coefficients are: C (n, 1), C (n, 2), C (n, 3) respectively, so there is: C (n, 1) + C (n, 3) = 2C (n, 2), that is, N + n (n-1) (n-2) / 6 = 2n (n-1) / 2, that is, 1 + (n-1) (n-2) / 6 = n-1n ^ 2-3n + 2 = 6n-12n ^ 2-9n + 14 = 0 (n-2) (N-7) = 0 because n > 2, otherwise there is no fourth term, so n = 7

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