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%I #11 Sep 22 2023 12:42:59
%S 1,1,1,1,1,1,1,2,9,37,121,331,793,1718,5163,32281,217921,1188709,
%T 5291353,20031170,66744741,267996541,2030569465,18368560519,
%U 138812739409,853152218102,4409607501927,19826125988257,99717123889777,871344991322017,9658479225877057
%N Expansion of e.g.f. exp(Sum_{k>=0} x^(6*k + 1) / (6*k + 1)!).
%C Number of partitions of n-set into blocks congruent to 1 mod 6.
%F a(0) = 1; a(n) = Sum_{k=0..floor((n-1)/6)} binomial(n-1,6*k) * a(n-6*k-1). - _Seiichi Manyama_, Sep 22 2023
%t nmax = 30; CoefficientList[Series[Exp[Sum[x^(6 k + 1)/(6 k + 1)!, {k, 0, nmax}]], {x, 0, nmax}], x] Range[0, nmax]!
%t a[n_] := a[n] = Sum[Boole[MemberQ[{1}, Mod[k, 6]]] Binomial[n - 1, k - 1] a[n - k], {k, 1, n}]; a[0] = 1; Table[a[n], {n, 0, 30}]
%t nmax = 30; CoefficientList[Series[Exp[x*HypergeometricPFQ[{}, {1/3, 1/2, 2/3, 5/6, 7/6}, x^6/46656]], {x, 0, nmax}], x] * Range[0, nmax]! (* _Vaclav Kotesovec_, Apr 15 2020 *)
%Y Cf. A000110, A003724, A306347, A333881, A333882.
%K nonn
%O 0,8
%A _Ilya Gutkovskiy_, Apr 08 2020