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%I #21 Sep 08 2022 08:45:43
%S 783,1567,2351,3135,3919,4703,5487,6271,7055,7839,8623,9407,10191,
%T 10975,11759,12543,13327,14111,14895,15679,16463,17247,18031,18815,
%U 19599,20383,21167,21951,22735,23519,24303,25087,25871,26655,27439,28223
%N 784n - 1.
%C The identity (784*n-1)^2-(784*n^2-2*n)*28^2=1 can be written as a(n)^2-A158398(n)*28^2=1.
%H Vincenzo Librandi, <a href="/A158399/b158399.txt">Table of n, a(n) for n = 1..10000</a>
%H E. J. Barbeau, <a href="http://www.math.toronto.edu/barbeau/home.html">Polynomial Excursions</a>, Chapter 10: <a href="http://www.math.toronto.edu/barbeau/hxpol10.pdf">Diophantine equations</a> (2010), pages 84-85 (row 15 in the first table at p. 85, case d(t) = t*(28^2*t-2)).
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F G.f.: x*(783+x)/(1-x)^2.
%F a(n) = 2*a(n-1)-a(n-2).
%t LinearRecurrence[{2,-1},{783,1567},50]
%t 784*Range[40]-1 (* _Harvey P. Dale_, Aug 18 2022 *)
%o (Magma) I:=[783, 1567]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];
%o (PARI) a(n) = 784*n - 1.
%Y Cf. A158398.
%K nonn,easy
%O 1,1
%A _Vincenzo Librandi_, Mar 18 2009
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