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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
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
Sequence in context: A364225 A256995 A249129 * A245708 A126917 A250471
KEYWORD
nonn
AUTHOR
Leroy Quet, Nov 29 2001
STATUS
approved

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)