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 A239435 Values of n for which the equation x^2 - 25*y^2 = n has integer solutions. 2
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified September 18 05:40 EDT 2021. Contains 347509 sequences. (Running on oeis4.)