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A074371 Sigmabonacci numbers: a(n)=a(n-1)+Sigma(a(n-2)). Sigma(n)=Sum of divisors of n. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..35.

EXAMPLE

a(9)=76=a(8)+Sigma(a(7))=40+(1+2+11+22)=40+36=76.

MATHEMATICA

nxt[{a_, b_}]:={b, b+DivisorSigma[1, a]}; NestList[nxt, {1, 1}, 40][[All, 1]] (* Harvey P. Dale, Apr 08 2019 *)

PROG

(PARI) a(n) = if (n == 1, 1, if (n == 2, 1, a(n-1) + sigma(a(n-2)))); \\ Michel Marcus, Aug 15 2013

CROSSREFS

Sequence in context: A127076 A137208 A049527 * A032202 A125702 A052817

Adjacent sequences:  A074368 A074369 A074370 * A074372 A074373 A074374

KEYWORD

easy,nonn

AUTHOR

Miklos Kristof, Sep 24 2002

EXTENSIONS

More terms from Michel Marcus, Aug 15 2013

STATUS

approved

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Last modified December 10 15:09 EST 2019. Contains 329896 sequences. (Running on oeis4.)