OFFSET
0,3
EXAMPLE
a(0) = 1: the empty word.
a(1) = 1: aaaaaa.
a(2) = 174: aaaaaabbbbbb, aaaaababbbbb, ..., baabababaabb, baababababab.
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jun 23 2012
STATUS
approved