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A125963
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a(n) = the n-th composite's smallest positive divisor which does not occur earlier in the sequence.
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0
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1, 2, 4, 3, 5, 6, 7, 15, 8, 9, 10, 21, 11, 12, 25, 13, 27, 14, 30, 16, 33, 17, 35, 18, 19, 39, 20, 42, 22, 45, 23, 24, 49, 50, 51, 26, 54, 55, 28, 57, 29, 60, 31, 63, 32, 65, 66, 34, 69, 70, 36, 37, 75, 38, 77, 78, 40, 81, 41, 84, 85, 43, 87, 44, 90, 91, 46, 93, 47, 95, 48, 98
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| This sequence is a permutation of the positive integers.
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EXAMPLE
| The 7th composite integer is 14. The divisors of 14 are 1,2,7,14. Of these, 1 and 2 occur among the first 6 terms of the sequence. So 7 is the lowest divisor of 14 which is missing from the first 6 terms of the sequence. Therefore a(7) = 7.
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MATHEMATICA
| f[l_List] := Block[{n = Length[l] + 1, c = 1, k = n}, While[k > 0, c++; While[PrimeQ[c], c++ ]; k--; ]; Append[l, First[Select[Divisors[c], FreeQ[l, # ] &]]]]; Nest[f, {}, 75] (*Chandler*)
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CROSSREFS
| Cf. A002808.
Sequence in context: A111269 A131042 A056019 * A107896 A107897 A133256
Adjacent sequences: A125960 A125961 A125962 * A125964 A125965 A125966
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Feb 03 2007
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EXTENSIONS
| Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 07 2007
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