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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.
2
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
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Apr 09 2014
STATUS
approved