A074371 Sigmabonacci numbers: a(n)=a(n-1)+Sigma(a(n-2)). Sigma(n)=Sum of divisors of n.

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

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