A309346 Sums of two refactorable numbers.

2, 3, 4, 9, 10, 11, 13, 14, 16, 17, 18, 19, 20, 21, 24, 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

Offset

1,1

Links

Table of n, a(n) for n=1..64.

Eric Weisstein's World of Mathematics, Refactorable Number

Example

3 is in the sequence since 3 = 1 + 2 and both 1 and 2 are refactorable (since d(1) = 1 | 1 and d(2) = 2 | 2).
4 is in the sequence since 4 = 2 + 2 and 2 is refactorable (since d(2) | 2).

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/2]}] > 0, n, {}], {n, 100}]]

Crossrefs

Cf. A033950.

Sequence in context: A081870 A165315 A284681 * A047339 A250483 A294485

Adjacent sequences: A309343 A309344 A309345 * A309347 A309348 A309349

Keyword

nonn

Author

Wesley Ivan Hurt, Jul 24 2019

Status

approved