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A191383 Integers n such that each of n, 2n and 3n is a sum of 2 distinct positive cubes. 2
2457, 15561, 19656, 25389, 39816, 66339, 124488, 157248, 203112, 248976, 307125, 318528, 420147, 530712, 685503, 842751, 995904, 1075032, 1257984, 1624896, 1791153, 1945125, 1991808, 2457000, 2548224, 3173625, 3270267 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..2605

FORMULA

{n: n in A024670 and 2n in A024670 and 3n in A024670}.

EXAMPLE

2457 is in the sequence because 2457 = 9^3+12^3, 2*2457 = 4914 = 1^3+17^3, 3*2457 = 7371 = 8^3+19^3 have at least one representation as a sum of two distinct positive cubes.

MAPLE

isA000578 := proc(n) option remember; local f; for f in ifactors(n)[2] do if op(2, f) mod 3 <> 0 then return false; end if; end do: true ; end proc:

isA024670 := proc(n) option remember ; local k, kc, k3 ; for k from 1 do k3 := k^3 ; kc := n-k^3 ; if kc <= k3 then return false; elif isA000578(kc) then return true; end if; end do: end proc:

isA191383 := proc(n) isA024670(n) and isA024670(2*n) and isA024670(3*n) ; end proc:

for n from 1 do if isA191383(n) then printf("%d, \n", n); end if; end do: # R. J. Mathar, Jun 03 2011

CROSSREFS

Cf. A024670, A191345, A191352.

Sequence in context: A225893 A043620 A282872 * A206409 A252013 A252105

Adjacent sequences:  A191380 A191381 A191382 * A191384 A191385 A191386

KEYWORD

nonn

AUTHOR

Zak Seidov, Jun 01 2011

STATUS

approved

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Last modified May 27 11:47 EDT 2022. Contains 354097 sequences. (Running on oeis4.)