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検索: 2, 3, 4, 7, 8, 15, 24, 60, 168, 480
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| A007497 |
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a(n) = sigma(a(n-1)).
(Formerly M0581)
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+20
8
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| 2, 3, 4, 7, 8, 15, 24, 60, 168, 480, 1512, 4800, 15748, 28672, 65528, 122880, 393192, 1098240, 4124736, 15605760, 50328576, 149873152, 371226240, 1710858240, 7926750720, 33463001088, 109760857440, 384120963072
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..200
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FORMULA
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Conjecture : (1/2)*log(n)<a(n+1)/a(n)<2*log(n) - Benoit Cloitre (benoit7848c(AT)orange.fr), May 08 2003
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MAPLE
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A007497 := proc(n) options remember; if n <= 0 then RETURN(2) else sigma(A007497(n-1)); fi; end;
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MATHEMATICA
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a[1] = 2; a[n_] := DivisorSigma[1, a[n - 1]]; Table[ a[n], {n, 1, 30} ]
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CROSSREFS
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Cf. A000005.
Sequence in context: A120611 A092063 A126850 this_sequence A126882 A006549 A159554
Adjacent sequences: A007494 A007495 A007496 this_sequence A007498 A007499 A007500
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com)
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| A126850 |
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a(n)=OrdinaryUnitarySigma(a(n-1)). |
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+20
1
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| 2, 3, 4, 7, 8, 15, 24, 60, 168, 480, 1512, 3360, 12096, 28448, 64512, 163760, 401760, 991872, 2399040, 6858000, 13999104, 32752000, 69400800, 172186560, 517867392, 1666990080, 5662137600, 14475575296, 33946612000, 73359820800, 158022774000
(list; graph; listen)
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OFFSET
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2,1
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FORMULA
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a(n)= A107749(a(n-1)). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 15 2008
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MAPLE
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A034448 := proc(n) local ifs, d ; if n = 1 then 1; else ifs := ifactors(n)[2] ; mul(1+ op(1, op(d, ifs))^op(2, op(d, ifs)), d=1..nops(ifs)) ; fi ; end: A006519 := proc(n) local i ; for i in ifactors(n)[2] do if op(1, i) = 2 then RETURN( op(1, i)^op(2, i) ) ; fi ; od: RETURN(1) ; end: A107749 := proc(n) local p2 ; p2 := A006519(n) ; numtheory[sigma](p2)*A034448(n/p2) ; end: A126850 := proc(n) option remember ; if n = 1 then 2; else A107749(A126850(n-1)) ; fi ; end: seq(A126850(n), n=1..40) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 15 2008
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CROSSREFS
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Cf. A107749, A126849.
Cf. A107749, A126849, A007497.
Sequence in context: A116961 A120611 A092063 this_sequence A007497 A126882 A006549
Adjacent sequences: A126847 A126848 A126849 this_sequence A126851 A126852 A126853
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KEYWORD
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nonn
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AUTHOR
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Yasutoshi Kohmoto zbi74583(AT)boat.zero.ad.jp, Feb 24 2007
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EXTENSIONS
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Edited and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 15 2008
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