cp's OEIS Frontend

A376831 Numbers k such that sigma(k + sigma(k)) = sigma(k) + sigma(sigma(k)), where sigma = A000203.

%I A376831 #20 Oct 07 2024 01:27:25
%S A376831 1986,58920,88092,111276,201588,662160,1103076,1573536,1671056,
%T A376831 1887900,3172434,4507152,4575124,8105188,10971936,42273728,56886840
%N A376831 Numbers k such that sigma(k + sigma(k)) = sigma(k) + sigma(sigma(k)), where sigma = A000203.
%e A376831 a(3) =  88092 is a term because sigma(88092) = 222768, sigma(222768) = 812448 and sigma(88092 + 222768) = sigma(310860) = 1035216 = 222768 + 812448.
%p A376831 filter:= proc(k) uses numtheory; local s;
%p A376831  s:= sigma(k);
%p A376831  sigma(k+s) = s + sigma(s)
%p A376831 end proc:
%p A376831 select(filter, [$1..10^7]);
%Y A376831 Cf. A000203, A376830, A376843, A376844, A376848, A376849, A376851.
%K A376831 nonn,more
%O A376831 1,1
%A A376831 _Robert Israel_, Oct 05 2024