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A074371
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Sigmabonacci numbers: a(n)=a(n-1)+Sigma(a(n-2)). Sigma(n)=Sum of divisors of n.
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0
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1, 1, 2, 3, 6, 10, 22, 40, 76, 166, 306, 558, 1260, 2508, 6876, 13596, 31068, 66012, 144636, 298692, 656532, 1411650, 3114050, 6907892, 12800744, 24982760, 51166280, 112488680, 239410280, 501240080, 1039913300, 2346376556, 4608703112, 8900121992, 18206157332
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OFFSET
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1,3
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LINKS
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EXAMPLE
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a(9)=76=a(8)+Sigma(a(7))=40+(1+2+11+22)=40+36=76.
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MATHEMATICA
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nxt[{a_, b_}]:={b, b+DivisorSigma[1, a]}; NestList[nxt, {1, 1}, 40][[All, 1]] (* Harvey P. Dale, Apr 08 2019 *)
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PROG
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(PARI) a(n) = if (n == 1, 1, if (n == 2, 1, a(n-1) + sigma(a(n-2)))); \\ Michel Marcus, Aug 15 2013
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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