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A309346 Numbers that are the sum of two refactorable numbers. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 1 04:58 EDT 2020. Contains 333155 sequences. (Running on oeis4.)