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 A118460 a(n) is the smallest positive integer which does not occur earlier in the sequence and where GCD(n(n+1)/2,a(n)) = 1. 2
 1, 2, 5, 3, 4, 8, 9, 7, 11, 6, 13, 17, 10, 16, 19, 15, 14, 20, 21, 23, 25, 12, 29, 31, 18, 22, 37, 27, 26, 28, 33, 35, 32, 24, 41, 43, 30, 34, 47, 39, 38, 40, 45, 49, 44, 36, 53, 55, 46, 52, 59, 51, 50, 56, 57, 61, 62, 42, 67, 71, 48, 58, 65, 63, 64, 68, 69, 73, 74, 54, 77, 79 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sequence is a permutation of the positive integers. LINKS Diana Mecum, Table of n, a(n) for n = 1..500 EXAMPLE Of the positive integers (6,7,8,...) not occurring among the first 5 terms of the sequence, 8 is the lowest coprime to 6*7/2 = 21. So a(6) = 8. a(6) is not 6 or 7 because GCD(6,21) > 1 and GCD(7,21) > 1. CROSSREFS Cf. A118461, A000217. Sequence in context: A105530 A245815 A105108 * A064788 A099521 A120238 Adjacent sequences:  A118457 A118458 A118459 * A118461 A118462 A118463 KEYWORD nonn AUTHOR Leroy Quet, Apr 28 2006 EXTENSIONS More terms from Diana L. Mecum, Jul 15 2007 STATUS approved

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Last modified August 20 07:48 EDT 2019. Contains 326143 sequences. (Running on oeis4.)