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A309347 Sums of two refactorable numbers whose difference is refactorable. 1

%I

%S 3,10,17,27,36,48,54,60,84,88,96,104,108,112,120,128,132,136,144,152,

%T 156,168,176,180,184,192,200,204,208,216,224,228,232,240,248,252,256,

%U 264,272,276,280,288,296,300,304,312,324,328,336,344,348,352,360,368

%N Sums of two refactorable numbers whose difference 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[(n - 2 i)/DivisorSigma[0, n - 2 i]] + Floor[(n - 2 i)/DivisorSigma[0, n - 2 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 - 1)/2]}] > 0, n, {}], {n, 400}]]

%Y Cf. A033950.

%K nonn

%O 1,1

%A _Wesley Ivan Hurt_, Jul 24 2019

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Last modified May 26 02:56 EDT 2020. Contains 334613 sequences. (Running on oeis4.)