The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A157368 a(n) = 49*n^2 - 78*n + 31. 3
 2, 71, 238, 503, 866, 1327, 1886, 2543, 3298, 4151, 5102, 6151, 7298, 8543, 9886, 11327, 12866, 14503, 16238, 18071, 20002, 22031, 24158, 26383, 28706, 31127, 33646, 36263, 38978, 41791, 44702, 47711, 50818, 54023, 57326, 60727, 64226 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The identity (2401*n^2-3822*n+1520)^2-(49*n^2-78*n+31)*( 343*n-273)^2=1 can be written as A157370(n)^2-a(n)*A157369(n)^2=1. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..10000 Vincenzo Librandi, X^2-AY^2=1 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). G.f: x*(-2-65*x-31*x^2)/(x-1)^3. E.g.f.: (31 - 29*x + 49*x^2)*exp(x) - 31. - G. C. Greubel, Feb 02 2018 MATHEMATICA LinearRecurrence[{3, -3, 1}, {2, 71, 238}, 40] PROG (MAGMA) I:=[2, 71, 238]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; (PARI) a(n) = 49*n^2 - 78*n + 31. CROSSREFS Cf. A157369, A157370. Sequence in context: A164554 A141908 A234298 * A095935 A202813 A081368 Adjacent sequences:  A157365 A157366 A157367 * A157369 A157370 A157371 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Feb 28 2009 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 21 19:57 EDT 2020. Contains 337273 sequences. (Running on oeis4.)