A373680 Expansion of e.g.f. exp(x / (1 - x^3)^2).
1, 1, 1, 1, 49, 241, 721, 16801, 204961, 1276129, 19968481, 417479041, 4522597201, 62399971921, 1685741065009, 28122880050721, 415551065616961, 12085752936331201, 281057646411506881, 4923299166925874689, 143004800073025326961, 4244797186148550210481
Offset: 0
Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n\3, binomial(2*n-5*k-1, k)/(n-3*k)!);
Formula
a(n) = n! * Sum_{k=0..floor(n/3)} binomial(2*n-5*k-1,k)/(n-3*k)!.
a(n) == 1 (mod 48).