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 A157889 a(n) = 18*n^2 + 1. 4
 19, 73, 163, 289, 451, 649, 883, 1153, 1459, 1801, 2179, 2593, 3043, 3529, 4051, 4609, 5203, 5833, 6499, 7201, 7939, 8713, 9523, 10369, 11251, 12169, 13123, 14113, 15139, 16201, 17299, 18433, 19603, 20809, 22051, 23329, 24643, 25993, 27379, 28801 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The identity (18n^2 + 1)^2 - (81n^2 + 9)*(2n)^2 = 1 can be written as a(n)^2 - A157888(n)*A005843(n+1)^2 = 1. - Vincenzo Librandi, Feb 05 2012 Sequence found by reading the line from 19, in the direction 19, 73, ... in the square spiral whose vertices are the generalized hendecagonal numbers A195160. - Omar E. Pol, Nov 05 2012 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 G.f: x*(19 + 16*x + x^2)/(1-x)^3. - Vincenzo Librandi, Feb 05 2012 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - Vincenzo Librandi, Feb 05 2012 MATHEMATICA LinearRecurrence[{3, -3, 1}, {19, 73, 163}, 40] (* Vincenzo Librandi, Feb 05 2012 *) PROG (MAGMA) I:=[19, 73, 163]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..50]]; // Vincenzo Librandi, Feb 05 2012 (PARI) for(n=1, 40, print1(18n^2 + 1", ")); \\ Vincenzo Librandi, Feb 05 2012 CROSSREFS Cf. A157888, A005843. Sequence in context: A154406 A141960 A178541 * A255897 A220447 A294460 Adjacent sequences:  A157886 A157887 A157888 * A157890 A157891 A157892 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Mar 08 2009 STATUS approved

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Last modified August 22 16:17 EDT 2019. Contains 326178 sequences. (Running on oeis4.)