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Nonnegative integers that are not the sum of two refactorable numbers whose difference is refactorable.
4

%I #28 Apr 20 2020 18:35:43

%S 0,1,2,4,5,6,7,8,9,11,12,13,14,15,16,18,19,20,21,22,23,24,25,26,28,29,

%T 30,31,32,33,34,35,37,38,39,40,41,42,43,44,45,46,47,49,50,51,52,53,55,

%U 56,57,58,59,61,62,63,64,65,66,67,68,69,70,71,72,73,74

%N Nonnegative integers that are not the sum 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, 0, 100}]]

%Y Cf. A033950, A309347.

%K nonn

%O 1,3

%A _Wesley Ivan Hurt_, Jul 27 2019