A309348 - OEIS

%I #10 Apr 20 2020 19:08:01

%S 2,3,9,10,11,13,14,17,19,20,21,25,36,37,38,41,42,44,49,52,57,58,60,61,

%T 64,65,68,72,73,76,80,81,84,85,88,89,92,96,97,98,100,104,105,108,109,

%U 113,116,117,120,124,126,128,129,132,133,136,137,140,144,145

%N Sums of two refactorable numbers whose product is refactorable.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/RefactorableNumber.html">Refactorable Number</a>

%t Flatten[Table[If[Sum[ (1 - Ceiling[(i (n - i))/DivisorSigma[0, i (n - i)]] + Floor[(i (n - i))/DivisorSigma[0, i (n - i)]]) (1 - Ceiling[i/DivisorSigma[0, i]] + Floor[i/DivisorSigma[0, i]]) (1 - Ceiling[(n - i)/DivisorSigma[0, n - i]] + Floor[(n - i)/DivisorSigma[0, n - i]]), {i, Floor[n/2]}] > 0, n, {}], {n, 150}]]

%Y Cf. A033950.

%K nonn

%O 1,1

%A _Wesley Ivan Hurt_, Jul 24 2019