A239435 Values of n for which the equation x^2 - 25*y^2 = n has integer solutions.

0, 1, 4, 9, 11, 16, 21, 24, 25, 31, 36, 39, 41, 44, 49, 51, 56, 61, 64, 69, 71, 75, 81, 84, 91, 96, 99, 100, 101, 104, 111, 119, 121, 124, 125, 129, 131, 136, 141, 144, 151, 156, 159, 161, 164, 169, 171, 175, 176, 181, 184, 189, 191, 196, 200, 201, 204, 211

Offset

1,3

Comments

This equation is a Pellian equation of the form x^2 - D^2*y^2 = N.

Links

Colin Barker, Table of n, a(n) for n = 1..1000

Example

21 is in the sequence because the equation x^2 - 25*y^2 = 21 has the solution (X,Y) = (11,2).

Prog

(PARI)
b(n) = sumdiv(n, f, f^2<=n && (n-f^2)%(10*f)==0) \\ See A239434
s=[]; for(n=0, 250, if(b(n)>0, s=concat(s, n))); s

Crossrefs

Cf. A042965, A230239, A230240, A239434.

Sequence in context: A312836 A312837 A190547 * A190559 A316621 A336826

Adjacent sequences: A239432 A239433 A239434 * A239436 A239437 A239438

Keyword

nonn

Author

Colin Barker, Mar 18 2014

Status

approved