A330725 a(0) = 0; thereafter a(n) = a(n-1) + sigma(n) if sigma(n) > a(n-1), otherwise a(n) = a(n-1) - sigma(n), where sigma is the sum of divisors function A000203.

0, 1, 4, 0, 7, 1, 13, 5, 20, 7, 25, 13, 41, 27, 3, 27, 58, 40, 1, 21, 63, 31, 67, 43, 103, 72, 30, 70, 14, 44, 116, 84, 21, 69, 15, 63, 154, 116, 56, 0, 90, 48, 144, 100, 16, 94, 22, 70, 194, 137, 44, 116, 18, 72, 192, 120, 0, 80, 170, 110, 278, 216, 120, 16

Offset

0,3

Links

Alois P. Heinz, Table of n, a(n) for n = 0..20000

Maple

a:= proc(n) option remember; `if`(n=0, 0, ((s, t)-> s+
      `if`(s<t, t, -t))(a(n-1), numtheory[sigma](n)))
    end:
seq(a(n), n=0..80);

Mathematica

nxt[{n_, a_}]:={n+1, If[DivisorSigma[1, n+1]>a, a+DivisorSigma[1, n+1], a- DivisorSigma[ 1, n+1]]}; NestList[nxt, {0, 0}, 70][[All, 2]] (* Harvey P. Dale, May 14 2022 *)

Crossrefs

Cf. A000203, A008344, A008345, A008348, A076042, A111466, A126646, A327442, A331165.

Sequence in context: A157698 A342360 A251967 * A057641 A352886 A336029

Adjacent sequences: A330722 A330723 A330724 * A330726 A330727 A330728

Keyword

nonn,look

Author

Alois P. Heinz, Jan 11 2020

Status

approved