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
Keywords
Examples
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.
Links
- Chai Wah Wu, Table of n, a(n) for n = 1..2605
Programs
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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
Comments