cp's OEIS Frontend

A250398 Composite numbers whose sum of divisors divides the sum of their unrelated numbers.

%I A250398 #17 Jan 13 2025 04:11:15
%S A250398 4,10,22,34,46,58,82,94,106,118,142,166,178,202,214,226,262,274,298,
%T A250398 334,346,358,382,394,454,466,478,493,502,514,526,538,562,586,622,634,
%U A250398 694,706,718,766,778,802,838,862,886,898,922,934,958,982,1006,1018,1042,1114
%N A250398 Composite numbers whose sum of divisors divides the sum of their unrelated numbers.
%C A250398 For a definition of unrelated number see A045763.
%C A250398 Most of the terms belong to A112774. First difference is at a(28) = 493.
%H A250398 Paolo P. Lava, <a href="/A250398/b250398.txt">Table of n, a(n) for n = 1..1000</a>
%e A250398 There is no unrelated number to 4. Therefore 0 / sigma(4) = 0 / 7 = 0 is an integer.
%e A250398 Unrelated numbers to 10 are 4, 6, 8 and their sum is 18. Now, 18 / sigma(10) = 18 / 18 = 1, that is an integer.
%p A250398 with(numtheory); P:=proc(q) local n;
%p A250398 for n from 1 to q do if not isprime(n) then
%p A250398 if type((1+n*(n+1)/2-sigma(n)-n*phi(n)/2)/sigma(n),integer)
%p A250398 then print(n); fi; fi; od; end: P(10^5);
%Y A250398 Cf. A000203, A045763, A066760, A112774, A250399.
%K A250398 nonn
%O A250398 1,1
%A A250398 _Paolo P. Lava_, Nov 21 2014