A393425 - OEIS

%I #10 Feb 18 2026 16:59:07

%S 16688,33592,49808,132928,213568,322660,495808,1826846464,3139477866

%N Numbers k such that sigma(k) = psi(k) + phi(k) + Omega(k)^4.

%e 16688 is a term since sigma(16688) = 37200 = 28800 + 7104 + 6^4 = psi(16688) + phi(16688) + Omega(16688)^4.

%o (PARI) isok(k) = {my(f = factor(k)); sigma(f) == prod(i=1, #f~, (f[i, 1]+1) * f[i, 1]^(f[i, 2]-1)) + eulerphi(f) + bigomega(f)^4;} \\ _Amiram Eldar_, Feb 14 2026

%Y Cf. A000203, A001615, A000010, A001222, A390049, A393229, A393230.

%K nonn,hard,more

%O 1,1

%A _S. I. Dimitrov_, Feb 14 2026

%E a(8)-a(9) from _Amiram Eldar_, Feb 14 2026