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A180709
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a(n) = sigma(n*a(n-1)) for n>1 with a(1)=1.
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0
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1, 3, 13, 98, 1026, 16940, 318402, 8751951, 138772480, 4323245864, 120795955200, 5325759445800, 253615827548160, 17175333492928512, 1074413211620474880, 76931332113306746880, 5820049307236627906560, 433263727052606574415872
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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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nxt[{n_, a_}]:={n+1, DivisorSigma[1, a(n+1)]}; NestList[nxt, {1, 1}, 20][[All, 2]] (* Harvey P. Dale, Apr 28 2018 *)
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PROG
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(PARI) a(n)=if(n==1, 1, sigma(n*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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