cp's OEIS Frontend

A245649 Numbers n such that the sum of the non-anti-divisors of n is a multiple of the sum of the anti-divisors of n.

%I A245649 #29 Mar 14 2018 03:48:21
%S A245649 3,5,12,27,39,41,48,63,324,1275,1599,2259,2304,3124,3724,14295,19464,
%T A245649 21659,40655,44659,262983,338064,485463,505407,686700,696795,898528,
%U A245649 1595384,10377100,12332927,14452991,14883967,21024479,23068975,25527535,30971420,37471143
%N A245649 Numbers n such that the sum of the non-anti-divisors of n is a multiple of the sum of the anti-divisors of n.
%C A245649 Like A066860 but using anti-divisors.
%H A245649 Lars Blomberg, <a href="/A245649/b245649.txt">Table of n, a(n) for n = 1..70</a>
%e A245649 The anti-divisors of 14295 are 2, 6, 10, 11, 23, 30, 113, 253, 1243, 1906, 2599, 5718, 9530 which sum is 21444. The sum of the non-anti-divisors is 14295*14296 / 2 - 21444 = 102159216 and 102159216 / 21444 = 4764.
%p A245649 with(numtheory):P:=proc(q) local a,j,k,n;
%p A245649 for n from 3 to q do
%p A245649 k:=0; j:=n; while j mod 2 <> 1 do k:=k+1; j:=j/2; od;
%p A245649 a:=sigma(2*n+1)+sigma(2*n-1)+sigma(n/2^k)*2^(k+1)-6*n-2;
%p A245649 if type(n*(n+1)/(2*a),integer) then print(n); fi;
%p A245649 od; end: P(10^10);
%Y A245649 Cf. A066272, A066860.
%K A245649 nonn
%O A245649 1,1
%A A245649 _Paolo P. Lava_, Aug 22 2014
%E A245649 a(28)-a(37) from _Lars Blomberg_, Oct 27 2014