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Search: id:A111426
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| A111426 |
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Difference between largest and smallest prime factor of the n-th composite number. |
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+0
3
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| 0, 1, 0, 0, 3, 1, 5, 2, 0, 1, 3, 4, 9, 1, 0, 11, 0, 5, 3, 0, 8, 15, 2, 1, 17, 10, 3, 5, 9, 2, 21, 1, 0, 3, 14, 11, 1, 6, 5, 16, 27, 3, 29, 4, 0, 8, 9, 15, 20, 5, 1, 35, 2, 17, 4, 11, 3, 0, 39, 5, 12, 41, 26, 9, 3, 6, 21, 28, 45, 14, 1, 5, 8, 3, 15, 11, 4, 51, 1, 9, 34, 5, 17, 18, 27, 10, 57, 10, 3, 0
(list; graph; listen)
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OFFSET
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1,5
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COMMENT
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a(n) = 0 iff the n-th composite number is a perfect power.
First occurrence of k or 0 if impossible: 2,8,5,12,7,38,0,21,13,26,16,61,0,35,22,40,25,84,0,49,31,156,0,111,0 ...,.
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FORMULA
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a(n) = A046665(A002808(n)). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 19 2008
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MATHEMATICA
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Composite[n_] := FixedPoint[n + 1 + PrimePi[ # ] &, n]; f[n_] := Block[{a = First@Transpose@FactorInteger@n}, a[[ -1]] - a[[1]]]; f[n_] := Block[{a = First@Transpose@FactorInteger@n}, a[[ -1]] - a[[1]]] (* Robert G. Wilson v *)
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CROSSREFS
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Sequence in context: A112031 A046531 A083722 this_sequence A100576 A131032 A130323
Adjacent sequences: A111423 A111424 A111425 this_sequence A111427 A111428 A111429
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KEYWORD
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nonn
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AUTHOR
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Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Nov 13 2005
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Nov 17 2005
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