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 A065561 a(1) = 1; for n >= 2, a(n) = (d(n)-1)-th highest positive integer that equals no a(k), 1 <= k < n, where d(n) is the number of positive divisors of n, A000005(n). 3
 1, 2, 3, 5, 4, 8, 6, 10, 9, 12, 7, 16, 11, 15, 17, 19, 13, 22, 14, 24, 21, 23, 18, 30, 25, 27, 28, 32, 20, 36, 26, 35, 33, 34, 37, 43, 29, 39, 40, 46, 31, 48, 38, 47, 49, 44, 41, 56, 45, 53, 51, 55, 42, 60, 54, 62, 57, 58, 50, 70, 52, 63, 66, 68, 64, 72, 59, 71, 67, 76, 61, 82 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Every positive integer occurs once and only once somewhere in this sequence. LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 EXAMPLE d(6)-1 = 3 and the 3rd-highest positive integer not equal to 1, 2, 3, 5, or 4 (the values of a(k) for 1 <= k < 6) is 8. MATHEMATICA With[{nn = 72}, Fold[Append[#1, Complement[Range[#2 + Ceiling[nn/6]], #1][[DivisorSigma[0, #2] - 1]]] &, {1}, Range[2, nn]]] (* Michael De Vlieger, Dec 11 2017 *) CROSSREFS Cf. A065578, A065562. Sequence in context: A255234 A256995 A249129 * A245708 A126917 A250471 Adjacent sequences:  A065558 A065559 A065560 * A065562 A065563 A065564 KEYWORD nonn AUTHOR Leroy Quet, Nov 29 2001 STATUS approved

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Last modified October 15 00:14 EDT 2019. Contains 328025 sequences. (Running on oeis4.)