A038862 Numbers ending with '7' that are the difference of two positive cubes.

7, 37, 117, 127, 217, 387, 397, 547, 657, 817, 1027, 1197, 1267, 1387, 1647, 1657, 1727, 2107, 2437, 2457, 2717, 2977, 3087, 3367, 3997, 4167, 4447, 4697, 4977, 5167, 5677, 5707, 6327, 6347, 6487, 6517, 7057, 7317, 7657, 7957, 8587, 8937, 9197, 9317

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

filter:= proc(n) local t, y, r;
  for t in sort(convert(numtheory:-divisors(n), list))  do
    r:= 12*n*t-3*t^4;
    if r < 0 then return false fi;
    if not issqr(r) then next fi;
    y:= (sqrt(r)-3*t^2)/(6*t);
    if y::posint then return true fi
  od;
  false
end proc:
select(filter, [seq(i, i=7..10000, 10)]); # Robert Israel, Aug 08 2019

Mathematica

With[{nn=60}, Select[Union[#[[2]]-#[[1]]&/@Subsets[Range[nn]^3, {2}]], Mod[#, 10] == 7&&#<nn^3-(nn-1)^3&]] (* Harvey P. Dale, Jan 12 2022 *)

Crossrefs

Cf. A181123.

Sequence in context: A106064 A369061 A282001 * A136204 A139891 A082113

Adjacent sequences: A038859 A038860 A038861 * A038863 A038864 A038865

Keyword

nonn,base

Author

Jeff Burch

Extensions

Name corrected by Robert Israel, Aug 08 2019

Status

approved