The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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 A339248 Adjacent sequences:  A073928 A073929 A073930 * A073932 A073933 A073934 KEYWORD more,nonn AUTHOR Jason Earls, Sep 03 2002 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 21 05:57 EST 2022. Contains 350473 sequences. (Running on oeis4.)