login
Nonnegative numbers of the form 6^x - y^2.
5

%I #35 Oct 14 2023 23:44:09

%S 0,1,2,5,6,11,20,27,32,35,36,47,71,72,95,116,135,140,152,167,180,191,

%T 200,207,212,215,216,272,335,380,396,431,455,512,551,567,620,671,720,

%U 767,812,855,860,887,896,935,972,1007,1040,1052,1071,1100,1127,1152

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

%C No integers congruent to {3,4,8,9} mod 10. - _Zak Seidov_, Nov 14 2011

%C 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

%H Hugo Pfoertner, <a href="/A051217/b051217.txt">Table of n, a(n) for n = 1..513</a>

%t 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 *)

%o (PARI) is_A051217(n) = !A200440(n) \\ _M. F. Hasler_, Nov 18 2011

%Y Cf. A201122.

%K nonn

%O 1,3

%A _David W. Wilson_