Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #19 Jul 30 2014 08:16:28
%S 1,1,4,27,252,3020,44220,765030,15269520,345376080,8730489600,
%T 243911883600,7463164262400,248207881521600,8915064168410400,
%U 343923449355486000,14182674669779616000,622591172035376544000,28986699477880400256000,1426677017904959524704000
%N Number of words of length n over the alphabet {0,...,n-1} that avoid the pattern 1111.
%H Alois P. Heinz, <a href="/A239368/b239368.txt">Table of n, a(n) for n = 0..350</a>
%F Recursion: see Maple program.
%p a:= proc(n) option remember; `if`(n<3, n^n,
%p ((105*n^3-252*n^2+175*n-36) *a(n-1) -2*(n-1)^2 *a(n-2)
%p +2*(5*n-2)*(n-1)^2*(n-2)^2*a(n-3)) / (4*(2*n-1)*(5*n-7)))
%p end:
%p seq(a(n), n=0..20); # _Alois P. Heinz_, Jul 20 2014
%Y Cf. A012244, A239295.
%K nonn
%O 0,3
%A _Chad Brewbaker_, Mar 17 2014
%E a(8)-a(11) from _Alois P. Heinz_, Mar 17 2014
%E a(12)-a(19) from _Alois P. Heinz_, Jul 20 2014