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A359808
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a(n) is the least prime factor of the alternating factorial n! - (n-1)! + (n-2)! - ... 1! for n > 2; a(1) = a(2) = 1.
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2
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1, 1, 5, 19, 101, 619, 4421, 35899, 79, 3301819, 13, 29, 47, 23, 1226280710981, 53, 47, 2683, 115578717622022981, 8969, 113, 79, 85439, 12203, 59, 1657, 127, 61, 661, 47, 173183, 1117, 83, 4729, 37, 103, 2858548279, 59, 67, 431, 32656499591185747972776747396512425885838364422981
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OFFSET
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1,3
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COMMENTS
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a(n) is the least prime factor of A005165(n) (unless A005165(n) = 1, in which case a(n) = 1).
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LINKS
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FORMULA
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MAPLE
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b:= proc(n) option remember; `if`(n=0, 0, n!-b(n-1)) end:
a:= n-> `if`(n<3, 1, min(numtheory[factorset](b(n)))):
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MATHEMATICA
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a[n_] := FactorInteger[AlternatingFactorial[n]][[1, 1]];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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