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

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);

Crossrefs

Cf. A052855.

Sequence in context: A148439 A151515 A264746 * A293743 A360274 A001444

Adjacent sequences: A052867 A052868 A052869 * A052871 A052872 A052873

Keyword

easy,nonn

Author

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

Extensions

More terms from Alois P. Heinz, Mar 16 2016

Status

approved