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A073931 Numbers n such that the sum of the anti-divisors of n = 2n. 2
77, 1568, 2768, 4775040 (list; graph; refs; listen; history; text; internal format)
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.

MAPLE

A073931:= proc(q) local a, k, n;

for n from 1 to q do

  a:=0; for k from 2 to n-1 do if abs((n mod k)-k/2)<1 then a:=a+k; fi; od;

  if a=2*n then print(n); fi; od; end:

A073931(10^10); # Paolo P. Lava, Mar 08 2013

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 A219126

Adjacent sequences:  A073928 A073929 A073930 * A073932 A073933 A073934

KEYWORD

more,nonn

AUTHOR

Jason Earls, Sep 03 2002

STATUS

approved

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Last modified June 4 11:09 EDT 2020. Contains 334825 sequences. (Running on oeis4.)