OFFSET
1,1
COMMENTS
A161917 is a subsequence of this sequence.
FORMULA
EXAMPLE
6-> sum divisors=sigma(6)=12; sum anti-divisors=4; 12/4=3.
30-> sum divisors=sigma(30)=72; sum anti-divisors=4+12+20=36; 72/36=2.
MAPLE
with(numtheory): P:=proc(i) local a, b, j, k, s, n;
for n from 3 to i do b:=divisors(n); s:=add(b[k], k=1..nops(b));
k:=0; j:=n; while j mod 2 <> 1 do k:=k+1; j:=j/2; od; a:=sigma(2*n+1)+sigma(2*n-1)+sigma(n/2^k)*2^(k+1)-6*n-2;
if type(s/a, integer) then print(n); fi; od; end: P(10^6);
MATHEMATICA
f[n_] := Total@ Cases[Range[2, n - 1], _?(Abs[Mod[n, #] - #/2] < 1 &)]; Select[Range[3, 10^3], Mod[DivisorSigma[1, #], f@ #] == 0 &] (* Michael De Vlieger, Oct 08 2015 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Jun 07 2011
EXTENSIONS
a(21)-a(36) from Donovan Johnson, Jun 24 2012
STATUS
approved