A373684 Expansion of e.g.f. exp(x / (1 - x^3)) / (1 - x^3).
1, 1, 1, 7, 49, 181, 1201, 16171, 122977, 971209, 16788961, 206578351, 2094314641, 40260673597, 694617709969, 9088535091091, 187060085419201, 4109646055718161, 68029103349383617, 1498126927153125079, 39199612737165358321, 799248202624341298501
Offset: 0
Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n\3, binomial(n-2*k, k)/(n-3*k)!);
Formula
a(n) = n! * Sum_{k=0..floor(n/3)} binomial(n-2*k,k)/(n-3*k)!.
a(n) == 1 (mod 6).