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Search: id:A130687
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| A130687 |
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Numbers n such that a_1! + a_2! + ... + a_m! is a square number, where a_1a_2...a_m is the decimal expansion of n. |
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+0
2
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| 1, 14, 15, 17, 22, 40, 41, 45, 50, 51, 54, 70, 71, 102, 112, 120, 121, 123, 132, 144, 156, 165, 200, 201, 203, 210, 211, 213, 230, 231, 302, 312, 320, 321, 334, 343, 404, 414, 433, 440, 441, 457, 475, 506, 516, 547, 560, 561, 574, 605, 615
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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A010052(A061602(a(n)))=1. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 12 2007
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EXAMPLE
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1! + 4! = 4! + 1! = 5^2, hence 14 and 41 are in the sequence.
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MAPLE
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A061602 := proc(n) local digs ; digs := convert(n, base, 10) ; add(factorial(op(i, digs)), i=1..nops(digs)) ; end: isA130687 := proc(n) issqr(A061602(n)) ; end: for n from 1 to 3000 do if isA130687(n) then printf("%d, ", n) ; fi ; od ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 12 2007
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MATHEMATICA
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Select[Range[755], IntegerQ[Sqrt[DigitCount[ # ][[10]]+Sum[DigitCount[ # ][[i]]*i!, {i, 1, 9}]]] &]
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CROSSREFS
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Adjacent sequences: A130684 A130685 A130686 this_sequence A130688 A130689 A130690
Sequence in context: A004455 A089838 A048125 this_sequence A136012 A038456 A075658
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KEYWORD
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base,nonn
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AUTHOR
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Aktar Yalcin (aktaryalcin(AT)msn.com), Jun 30 2007
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EXTENSIONS
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Edited by Stefan Steinerberger (stefan.steinerberger(AT)gmail.com) and R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 12 2007
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