A211279 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 2] as of [1, 3].

1, 3, 7, 15, 33, 81, 223, 651, 1915, 5559, 15921, 45333, 129309, 371025, 1071411, 3108951, 9047853, 26374005, 76959295, 224790195, 657326803, 1924486719, 5641225341, 16554458025, 48627650779, 142963972275, 420635073625, 1238489452437, 3648942571185, 10757537699373, 31733207206191

Offset

0,2

Links

Table of n, a(n) for n=0..30.

Shalosh B. Ekhad and Doron Zeilberger, Automatic Solution of Richard Stanley's Amer. Math. Monthly Problem #11610 and ANY Problem of That Type, arXiv preprint arXiv:1112.6207, 2011. See subpages for rigorous derivations of g.f., recurrence, asymptotics for this sequence.

Crossrefs

Sequence in context: A136029 A225338 A101892 * A351660 A199882 A147102

Adjacent sequences: A211276 A211277 A211278 * A211280 A211281 A211282

Keyword

nonn

Author

N. J. A. Sloane, Apr 07 2012

Status

approved