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Search: id:A120690
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| A120690 |
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Number of ordered finite sequences a_1 <= a_2 <= ... <= a_n of length n of positive integers less than or equal to n whose product is n!. |
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+0
2
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| 1, 1, 1, 2, 2, 6, 6, 13, 33, 97, 97, 306, 306, 896, 2804, 7974, 7974, 24929, 24929, 82612, 263913, 782310, 782310
(list; graph; listen)
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OFFSET
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1,4
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EXAMPLE
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a(5)=2 because 5! = 1*2*3*4*5 = 2*2*2*3*5
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PROGRAM
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(PARI) a(n) = (b(c, p, m) = local(x); if(c<=0||m<=1||p>m^c, p==1, x=valuation(p, m); sum(i=x*isprime(m), x, b(c-i, p/m^i, m-1)))); b(n, n!, n)
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CROSSREFS
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Cf. A119551.
Sequence in context: A110660 A139550 A060549 this_sequence A056453 A034422 A071908
Adjacent sequences: A120687 A120688 A120689 this_sequence A120691 A120692 A120693
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KEYWORD
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more,nonn
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AUTHOR
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Martin Fuller (martin_n_fuller(AT)btinternet.com), Jun 26 2006
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