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A055486
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Number of solutions to sigma(x) = n!.
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4
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1, 0, 1, 3, 4, 15, 33, 111, 382, 1195, 3366, 14077, 53265, 229603, 910254, 4524029, 18879944, 91336498, 561832582, 2801857644, 14652294729, 78894985156, 408373652461, 2378940665083, 11939275822636, 71931330299023, 392274481206066, 2626331088771946
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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REFERENCES
| R. K. Guy (1981): Unsolved Problems In Number Theory, B39.
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FORMULA
| a(n) = A054973(n!) = Cardinality[{x; A000203(x) = A000142(n)}]
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EXAMPLE
| For n = 9, solutions to sigma(x) = n! = 362880 form a set {97440, ..., 361657} of size 382, so a(9) = 382.
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MAPLE
| with(numtheory):for f from 1 to 9 do fac := f!: k := 0:for n from 1 to fac do if sigma(n)=fac then k := k+1: fi: od: print( k); od:
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CROSSREFS
| Cf. A000142, A000203, A054973, A014197, A055488, A055489, A055506
Sequence in context: A024858 A135100 A205485 * A041665 A052133 A127144
Adjacent sequences: A055483 A055484 A055485 * A055487 A055488 A055489
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jun 28 2000
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EXTENSIONS
| More terms from Jud McCranie (JudMcCranie(AT)ugaalum.uga.edu), Oct 09 2000
a(13)-a(14) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Nov 22 2008
a(15) from Ray Chandler (rayjchandler(AT)sbcglobal.net), Jan 13 2009
a(16)-a(28) from Max Alekseyev (maxale(AT)gmail.com), Jan 23 2012
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