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
Links
- Alois P. Heinz, Table of n, a(n) for n = 0..20000
Programs
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Maple
a:= proc(n) option remember; `if`(n=0, 0, ((s, t)-> s+ `if`(s -
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 *)