A073931 Numbers n such that the sum of the anti-divisors of n = 2n.

77, 1568, 2768, 4775040

Offset

1,1

Comments

See A066272 for definition of anti-divisor.

a(5) > 10^10 - Hiroaki Yamanouchi, Mar 18 2015

Links

Table of n, a(n) for n=1..4.

Mathematica

antiDivisorSum[n_] := Total[Select[Range[2, n - 1], Abs[Mod[n, #] - #/2] < 1 &]]
Select[Range[1, 1600], antiDivisorSum[#] == 2*# &] (* Julien Kluge, Sep 19 2016 *)

Prog

(Python)
from sympy import divisors
A073931 = [n for n in range(3, 10**5) if sum([2*d for d in divisors(n) if n > 2*d and n % (2*d)] + [d for d in divisors(2*n-1) if n > d >=2 and n % d] + [d for d in divisors(2*n+1) if n > d >=2 and n % d]) == 2*n]
# Chai Wah Wu, Aug 13 2014

Crossrefs

Cf. A066417.

Sequence in context: A093277 A217643 A205603 * A296989 A105253 A339248

Adjacent sequences: A073928 A073929 A073930 * A073932 A073933 A073934

Keyword

more,nonn

Author

Jason Earls, Sep 03 2002

Status

approved