cp's OEIS Frontend

A321036 Number of words of length 3n such that all letters of the senary alphabet occur at least once and are introduced in ascending order and which can be built by repeatedly inserting triples of identical letters into the initially empty word.

%I A321036 #4 Oct 26 2018 16:19:49
%S A321036 1428,122094,6577494,288152280,11263151718,410775452736,
%T A321036 14329297278912,485304167135463,16110681501126303,527563895500327686,
%U A321036 17115058041339933282,551744934193726332360,17712851478876415128930,567151641983253355425936,18132410018268844312487352
%N A321036 Number of words of length 3n such that all letters of the senary alphabet occur at least once and are introduced in ascending order and which can be built by repeatedly inserting triples of identical letters into the initially empty word.
%H A321036 Alois P. Heinz, <a href="/A321036/b321036.txt">Table of n, a(n) for n = 6..659</a>
%p A321036 b:= (n, k)-> `if`(n=0, 1, k/n*add(binomial(3*n, j)*(n-j)*(k-1)^j, j=0..n-1)):
%p A321036 a:= n-> (k-> add((-1)^i*b(n, k-i)/(i!*(k-i)!), i=0..k))(6):
%p A321036 seq(a(n), n=6..25);
%Y A321036 Column k=6 of A256311.
%K A321036 nonn
%O A321036 6,1
%A A321036 _Alois P. Heinz_, Oct 26 2018