OFFSET
0,4
COMMENTS
Original name: A simple grammar.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..200
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 704
FORMULA
E.g.f.: log(1/(1-x))^3.
Recurrence: {a(1)=0, a(0)=0, a(2)=0, a(3)=6, (-1 - 3*n - 3*n^2 - n^3)*a(n+1) + (9*n + 7 + 3*n^2)*a(n+2) + (-6 - 3*n)*a(n+3) + a(n+4)}.
a(n) = stirling1(n, 3)*3!*(-1)^(n+1). - Leonid Bedratyuk, Aug 07 2012
a(n) = 6*A000399(n). - Andrew Howroyd, Jul 27 2020
MAPLE
spec := [S, {B=Cycle(Z), S=Prod(B, B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
with(combinat):seq(stirling1(j, 3)*3!*(-1)^(j+1), j=0..50); # Leonid Bedratyuk, Aug 07 2012
PROG
(PARI) a(n) = {3!*stirling(n, 3, 1)*(-1)^(n+1)} \\ Andrew Howroyd, Jul 27 2020
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
INRIA Encyclopedia of Combinatorial Structures, Jan 25 2000
EXTENSIONS
Name changed and terms a(20) and beyond from Andrew Howroyd, Jul 27 2020
STATUS
approved
