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Search: id:A133952
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| A133952 |
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a(n) = the number of "isolated divisors" of n!. A positive divisor, k, of n is isolated if neither (k-1) nor (k+1) divides n. |
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+0
2
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| 1, 0, 1, 4, 10, 19, 43, 77, 137, 243, 497, 749, 1520, 2518, 3952, 5294, 10628, 14564, 29199, 40855, 60605, 95786, 191700, 242580, 339732, 531896, 677048, 916946, 1834106, 2332346, 4664982, 5528982, 7863685, 12164443, 16422235, 19594843
(list; graph; listen)
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OFFSET
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1,4
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LINKS
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Ray Chandler, Table of n, a(n) for n=1..50
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FORMULA
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a(n) = A027423(n) - A133951(n) = A132881(A000142(n)).
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MAPLE
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A133952 := proc(n) local divs, k, i, a ; divs := sort(convert(numtheory[divisors](n!), list)) ; a := 0 ; for i from 1 to nops(divs) do k := op(i, divs) ; if not k-1 in divs and not k+1 in divs then a := a+1 ; fi ; od: RETURN(a) ; end: for n from 1 do printf("%d, ", A133952(n)) ; od: - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 19 2007
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CROSSREFS
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Cf. A133951, A027423.
Sequence in context: A057318 A008118 A097116 this_sequence A086176 A015789 A145021
Adjacent sequences: A133949 A133950 A133951 this_sequence A133953 A133954 A133955
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.com), Sep 30 2007
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EXTENSIONS
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Corrected and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 19 2007
a(26)-a(35) from Ray Chandler (rayjchandler(AT)sbcglobal.net), May 28 2008
a(36)-a(50) from Ray Chandler (rayjchandler(AT)sbcglobal.net), Jun 20 2008
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