A243171 Nonnegative integers of the form 2*x^2+5*x*y-5*y^2.
0, 2, 5, 7, 8, 13, 18, 20, 28, 32, 37, 45, 47, 50, 52, 58, 63, 67, 70, 72, 73, 80, 83, 97, 98, 112, 117, 122, 125, 128, 130, 137, 145, 148, 158, 162, 163, 167, 175, 180, 182, 188, 193, 197, 200, 202, 203, 208, 223, 227, 232, 242, 245, 252, 262, 268, 278, 280, 288, 292, 293, 305, 307, 317, 320, 325, 332, 333, 338, 343, 353, 358, 362, 370, 377, 382, 383
Offset: 1
Keywords
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1500
- N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)
Crossrefs
Primes in this sequence = A141112.
Programs
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Mathematica
Module[{k,r},Reap[For[k=1,k<=100,k++,r=Reduce[k==2*x^2+5*x y-5* y^2,{x,y},Integers];If[r=!=False,(*Print[k," ",r];*)Sow[k]]]][[2,1]]] (* Vincenzo Librandi, Nov 16 2024 *) sol[t_]:=Solve[2*x^2+5*x*y-5*y^2==t,{x,y},Integers]; Select[Range[0,385],sol[#]!={}&] (* Vincenzo Librandi, Nov 25 2024 *)
Extensions
Missing a(63)=307 inserted by Vincenzo Librandi, Dec 08 2024
Comments