A033832 Sum of odd divisors of n < sqrt(n) = sum of even divisors of n < sqrt(n).

1, 40, 100, 208, 928, 1044, 3904, 10692, 17444, 29524, 36652, 45980, 87604, 91044, 136808, 158652, 161564, 171028, 187068, 218652, 230044, 260608, 287868, 406812, 438124, 450492, 583110, 665684, 719550, 731850, 736648, 865444, 1045504

Offset: 1

Author

Naohiro Nomoto

Keywords

• easy
• nonn

Comments

All terms except first one appear to be even. - Michel Marcus, Jul 15 2013

Links

• Amiram Eldar, Table of n, a(n) for n = 1..500
• kaleidoscopic numbers [broken link]

Crossrefs

Cf. A070039, A113184.

Programs

Mathematica

aQ[n_] := DivisorSum[n, # * (-1)^# &, # < Sqrt[n] & ] == 0; Select[Range[10^4], aQ] (* Amiram Eldar, Sep 23 2019 *)

PARI

isok(n) = {so = 0; se = 0; fordiv (n, d, if (d < sqrt(n), if (d % 2, so += d, se += d))); return (so == se);} \\ Michel Marcus, Jul 14 2013

Extensions

Prepended a(1)=1, Michel Marcus, Jul 15 2013