A052870 - OEIS

A052870

A simple grammar.

1, 1, 2, 6, 15, 44, 128, 386, 1179, 3679, 11601, 37030, 119262, 387325, 1266647, 4168264, 13791565, 45856091, 153134306, 513403575, 1727395042, 5830866601, 19740613869, 67014421326, 228066659185, 777961702283, 2659398743509, 9109015516017, 31258117755635

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OFFSET

0,3

LINKS

Table of n, a(n) for n=0..28.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 841

FORMULA

From Seiichi Manyama, Jun 07 2023: (Start)

Conjectures: G.f. satisfies A(x) = exp( Sum_{k>=1} (-1)^(k+1) * A(x^k) * x^k/(k * (1 - x^k)) ).

A(x) = Sum_{k>=0} a(k) * x^k = Product_{j>=1} Product_{k>=0} (1+x^(j+k))^a(k). (End)

MAPLE

spec := [S, {C=Sequence(Z, 1 <= card), S=PowerSet(B), B=Prod(C, S)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);