OFFSET
0,3
COMMENTS
Permuting the symbols will not change the structure.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..1000
EXAMPLE
The a(1) = 1 word is 1.
The a(2) = 2 words are 11, 12.
The a(3) = 4 words are 111, 112, 122, 123.
The a(4) = 9 words are 1111, 1112, 1121, 1122, 1211, 1222, 1123, 1223, 1233.
PROG
(PARI) \\ See A351641 for R, S.
seq(n)={my(q=S(n), c=3); concat([1], sum(k=1, c, R(q^k-1)*sum(r=k, c, binomial(r, k)*(-1)^(r-k)/r!) )); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Feb 16 2022
STATUS
approved