cp's OEIS Frontend

A320204 Number of sets of nonempty words with a total of n letters over ternary alphabet such that all letters occur at least once in the set.

%I A320204 #7 Oct 07 2018 14:39:00
%S A320204 13,105,588,2811,12354,51543,207846,818241,3165036,12078462,45602379,
%T A320204 170665569,633997185,2340201492,8589679914,31370151073,114045173001,
%U A320204 412880470680,1489008227689,5350719651144,19163305147338,68416338358689,243533302332309,864441624894750
%N A320204 Number of sets of nonempty words with a total of n letters over ternary alphabet such that all letters occur at least once in the set.
%H A320204 Alois P. Heinz, <a href="/A320204/b320204.txt">Table of n, a(n) for n = 3..1000</a>
%p A320204 h:= proc(n, i, k) option remember; `if`(n=0, 1, `if`(i<1, 0,
%p A320204       add(h(n-i*j, i-1, k)*binomial(k^i, j), j=0..n/i)))
%p A320204     end:
%p A320204 a:= n-> (k-> add((-1)^i*binomial(k, i)*h(n$2, k-i), i=0..k))(3):
%p A320204 seq(a(n), n=3..30);
%Y A320204 Column k=3 of A319501.
%Y A320204 Cf. A320213.
%K A320204 nonn
%O A320204 3,1
%A A320204 _Alois P. Heinz_, Oct 07 2018