OFFSET
0,7
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 736
FORMULA
E.g.f.: log(-1/(-1+x))^6.
Recurrence: {a(1)=0, a(0)=0, a(2)=0, a(4)=0, a(3)=0, a(5)=0, a(6)=720, (1+15*n^2+6*n+6*n^5+15*n^4+20*n^3+n^6)*a(n+1) + (-63-186*n-225*n^2-6*n^5-45*n^4-140*n^3)*a(n+2) + (540*n+120*n^3+375*n^2+15*n^4+301)*a(n+3) + (-390*n-20*n^3-350-150*n^2)*a(n+4) + (140+15*n^2+90*n)*a(n+5) + (-21-6*n)*a(n+6) + a(n+7)}.
a(n) = 720*A001233(n) = 6!*(-1)^n*Stirling1(n,6). - Andrew Howroyd, Jul 27 2020
MAPLE
spec := [S, {B=Cycle(Z), S=Prod(B, B, B, B, B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
PROG
(PARI) a(n) = {6!*stirling(n, 6, 1)*(-1)^n} \\ Andrew Howroyd, Jul 27 2020
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
Name changed and terms a(20) and beyond from Andrew Howroyd, Jul 27 2020
STATUS
approved