login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A309351 Sums of two distinct refactorable numbers whose product and difference are refactorable. 0
3, 10, 17, 36, 60, 84, 88, 96, 104, 108, 132, 136, 144, 152, 156, 168, 180, 184, 192, 204, 208, 216, 228, 232, 240, 248, 252, 264, 276, 288, 296, 300, 312, 324, 328, 336, 344, 348, 352, 372, 376, 384, 392, 396, 400, 408, 420, 424, 444, 456, 459, 468, 472 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..53.

Eric Weisstein's World of Mathematics, Refactorable Number

MATHEMATICA

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 (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, 500}]]

CROSSREFS

Cf. A033950.

Sequence in context: A309347 A273235 A334964 * A003615 A043293 A208894

Adjacent sequences:  A309348 A309349 A309350 * A309352 A309353 A309354

KEYWORD

nonn

AUTHOR

Wesley Ivan Hurt, Jul 24 2019

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 6 10:52 EDT 2020. Contains 334841 sequences. (Running on oeis4.)