A308421 Sums of two distinct refactorable numbers.

3, 9, 10, 11, 13, 14, 17, 19, 20, 21, 25, 26, 27, 30, 32, 33, 36, 37, 38, 41, 42, 44, 45, 48, 49, 52, 54, 57, 58, 60, 61, 62, 64, 65, 68, 69, 72, 73, 74, 76, 78, 80, 81, 82, 84, 85, 86, 88, 89, 90, 92, 93, 96, 97, 98, 100, 102, 104, 105, 106, 108, 109, 110

Offset

1,1

Links

Table of n, a(n) for n=1..63.

Eric Weisstein's World of Mathematics, Refactorable Number

Mathematica

Flatten[Table[If[Sum[ (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, 100}]]

Crossrefs

Cf. A033950.

Sequence in context: A329560 A330296 A043048 * A309349 A024574 A119203

Adjacent sequences: A308418 A308419 A308420 * A308422 A308423 A308424

Keyword

nonn

Author

Wesley Ivan Hurt, Jul 24 2019

Status

approved