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A309349 Sums of two distinct refactorable numbers whose product is refactorable. 0
3, 9, 10, 11, 13, 14, 17, 19, 20, 21, 25, 36, 37, 38, 41, 42, 44, 49, 52, 57, 58, 60, 61, 64, 65, 68, 72, 73, 76, 80, 81, 84, 85, 88, 89, 92, 96, 97, 98, 100, 104, 105, 108, 109, 113, 116, 117, 124, 126, 128, 129, 132, 133, 136, 137, 140, 144, 145, 148, 152 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..60.

Eric Weisstein's World of Mathematics, Refactorable Number

MATHEMATICA

Flatten[Table[If[Sum[ (1 - Ceiling[(i (n - i))/DivisorSigma[0, i (n - i)]] + Floor[(i (n - i))/DivisorSigma[0, i (n - 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, 150}]]

CROSSREFS

Cf. A033950.

Sequence in context: A330296 A043048 A308421 * A024574 A119203 A115403

Adjacent sequences:  A309346 A309347 A309348 * A309350 A309351 A309352

KEYWORD

nonn

AUTHOR

Wesley Ivan Hurt, Jul 24 2019

STATUS

approved

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Last modified May 30 23:58 EDT 2020. Contains 334747 sequences. (Running on oeis4.)