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A180707
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a(n) = sigma(2*a(n-1)) for n>1 with a(1)=1.
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2
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1, 3, 12, 60, 360, 2418, 12544, 58311, 299520, 2235324, 14515200, 122882760, 1152592896, 8365593600, 81041688000, 812657664000, 8244072345600, 78851793162240, 701965262389248, 5040363458592000, 49476663690854400
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OFFSET
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1,2
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LINKS
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MATHEMATICA
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NestList[DivisorSigma[1, 2#]&, 1, 20] (* Harvey P. Dale, Jan 12 2018 *)
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PROG
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(PARI) a(n)=if(n==1, 1, sigma(2*a(n-1)))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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