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A211291
a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 1, 2] as of [1, 3, 1].
0
1, 3, 9, 25, 69, 192, 537, 1508, 4249, 12009, 34044, 96795, 275989, 789040, 2261594, 6497986, 18712521, 54002913, 156162531, 452435327, 1313117536, 3817402150, 11114803333, 32408592752, 94623871921, 276620070867, 809602760028, 2372089156969, 6957106088502, 20423727601032, 60009849519354
OFFSET
0,2
LINKS
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: A098182 A211300 A211293 * A211294 A211297 A370227
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 07 2012
STATUS
approved