A240610 Number of n-length words w over a 4-ary alphabet such that w is empty or a prefix z concatenated with letter a_i and i=1 or 0 < #(z,a_{i-1}) >= #(z,a_i), where #(z,a_i) counts the occurrences of the i-th letter in z.

1, 1, 2, 5, 14, 45, 149, 509, 1756, 6082, 21246, 74125, 260940, 917060, 3251573, 11514563, 41115372, 146687475, 527318119, 1894548198, 6853413645, 24782205276, 90165044683, 327958242274, 1199475359682, 4386106532923, 16118279172044, 59223681674225

Offset

0,3

Links

Alois P. Heinz and Vaclav Kotesovec, Table of n, a(n) for n = 0..1000 (first 175 terms from Alois P. Heinz)

Vaclav Kotesovec, Recurrence (of order 6)

Formula

a(n) ~ 8465 * 4^n / (18 * Pi * n^3). - Vaclav Kotesovec, Aug 28 2014

Crossrefs

Column k=4 of A240608.

Sequence in context: A060996 A134378 A101226 * A149887 A149888 A149889

Adjacent sequences: A240607 A240608 A240609 * A240611 A240612 A240613

Keyword

nonn

Author

Alois P. Heinz, Apr 09 2014

Status

approved