cp's OEIS Frontend

A321040 Number of words of length 3n such that all letters of the denary 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 A321040 #4 Oct 26 2018 16:41:12
%S A321040 1430715,385671000,59757446980,7005490433656,691555233881785,
%T A321040 60757817462444531,4909804407096952946,372791285261732999200,
%U A321040 26986460830582840320825,1882051044395835159556710,127426007577261157375345878,8424538202077517861490125956
%N A321040 Number of words of length 3n such that all letters of the denary 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 A321040 Alois P. Heinz, <a href="/A321040/b321040.txt">Table of n, a(n) for n = 10..566</a>
%p A321040 b:= (n, k)-> `if`(n=0, 1, k/n*add(binomial(3*n, j)*(n-j)*(k-1)^j, j=0..n-1)):
%p A321040 a:= n-> (k-> add((-1)^i*b(n, k-i)/(i!*(k-i)!), i=0..k))(10):
%p A321040 seq(a(n), n=10..25);
%Y A321040 Column k=10 of A256311.
%K A321040 nonn
%O A321040 10,1
%A A321040 _Alois P. Heinz_, Oct 26 2018