The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A211297 a(n) = number of n-lettered words in the alphabet {1, 2, 3} with as many occurrences of the substring (consecutive subword) [1, 2, 1] as of [1, 3, 1]. 1
 1, 3, 9, 25, 69, 195, 555, 1573, 4457, 12677, 36165, 103323, 295639, 847587, 2434755, 7006089, 20193261, 58296927, 168567687, 488155597, 1415686337, 4111268669, 11955274925, 34808988199, 101471734355, 296139036809, 865204909777, 2530413173787, 7407817001559, 21706686476055, 63662015359655 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..1000 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: A211293 A211291 A211294 * A297590 A244934 A291594 Adjacent sequences:  A211294 A211295 A211296 * A211298 A211299 A211300 KEYWORD nonn AUTHOR N. J. A. Sloane, Apr 07 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 7 09:15 EST 2021. Contains 349574 sequences. (Running on oeis4.)