OFFSET
1,3
COMMENTS
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..800
FORMULA
EXAMPLE
0 is a term because there is only one length minimal language with 0 words: {}.
1 is a term: {a}.
3 is a term: {a, aa, ab}.
7 is a term: {a, aa, ab, aaa, aab, aba, abc}.
17 is a term: {a, aa, ab, aaa, aab, aba, abc, aaaa, aaab, aaba, aabb, aabc, abaa, abab, abac, abca, abcd}.
MAPLE
a:= proc(n) option remember; `if`(n<4, n*(n-1)/2,
2*a(n-1)+(n-3)*a(n-2)-(n-2)*a(n-3))
end:
seq(a(n), n=1..30);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 23 2017
STATUS
approved