A051217 Nonnegative numbers of the form 6^x - y^2.

0, 1, 2, 5, 6, 11, 20, 27, 32, 35, 36, 47, 71, 72, 95, 116, 135, 140, 152, 167, 180, 191, 200, 207, 212, 215, 216, 272, 335, 380, 396, 431, 455, 512, 551, 567, 620, 671, 720, 767, 812, 855, 860, 887, 896, 935, 972, 1007, 1040, 1052, 1071, 1100, 1127, 1152

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

No integers congruent to {3,4,8,9} mod 10. - Zak Seidov, Nov 14 2011

If k is not in this sequence, then A200440 gives the least modulus which proves that there cannot be a solution to k = 6^x - y^2. - M. F. Hasler, Nov 18 2011

Links

• Hugo Pfoertner, Table of n, a(n) for n = 1..513

Crossrefs

Cf. A201122.

Programs

Mathematica

max = 10^5; Clear[f]; f[m_] := f[m] = Select[Table[6^x - y^2, {x, 0, m}, {y, 0, Ceiling[6^(x/2)]}] // Flatten // Union, 0 <= # <= max &]; f[1]; f[m = 2]; While[f[m] != f[m - 1], m++]; Print["m = ", m]; A051217 = f[m] (* Jean-François Alcover, May 13 2017 *)

PARI

is_A051217(n) = !A200440(n)  \\ M. F. Hasler, Nov 18 2011