A191383 Integers n such that each of n, 2n and 3n is a sum of 2 distinct positive cubes.

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

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