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 A165137 a(n) is the number of patterns for n-character papaya words in an infinite alphabet. 8
 1, 1, 2, 4, 10, 21, 50, 99, 250, 454, 1242, 2223, 6394, 11389, 35002, 62034, 202010, 359483, 1233518, 2203507, 7944110, 14249736, 53811584, 96912709, 382289362, 691110821, 2841057442, 5154280744, 22033974854, 40105797777, 177946445580 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Papaya words are concatenations of two palindromes or palindromes themselves. A165136 is the number of papaya patterns for n-digit numbers. Thus a(n) coincides with A165136 for small n, and is greater than A165136 for larger n. The actual number of n-digit papaya numbers is A165135. The first 19 terms of this sequence are the same as in A165136. A165137(20) = A165136(20)+10. - Tanya Khovanova, Oct 01 2009, corrected by Franklin T. Adams-Watters, Apr 10 2011 LINKS Andrew Howroyd, Table of n, a(n) for n = 0..100 Chuan Guo, J. Shallit, A. M. Shur, On the Combinatorics of Palindromes and Antipalindromes, arXiv preprint arXiv:1503.09112 [cs.FL], 2015. Tanya Khovanova, Papaya Words and Numbers FORMULA a(n) = R(n) - Sum_{d|n,d

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Last modified December 13 08:50 EST 2018. Contains 318082 sequences. (Running on oeis4.)