OFFSET
0,3
EXAMPLE
a(0) = 1: the empty word.
a(1) = 1: a.
a(2) = 3: aabb, abab, baab.
a(3) = 106: aaabbbccc, aaabbcbcc, aaabbccbc, ..., cbaababcc, cbaabacbc, cbaabcabc.
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jun 23 2012
STATUS
approved