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%I #7 Apr 01 2019 02:58:34
%S 1,20,319,5084,81025,1291316,20580031,327989180,5227246849,
%T 83307960404,1327700119615,21159893953436,337230603135361,
%U 5374529756212340,85655245496262079,1365109398183980924,21756095125447432705,346732412608974942356,5525962506618151644991
%N Second class of all proper positive solutions y2(n) = a(n) of the Pell equation x^2 - 7*y^2 = 9.
%C The corresponding x2 solutions are given in A307172.
%C See A307172 for details.
%H <a href="/index/Ch#Cheby">Index entries for sequences related to Chebyshev polynomials.</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (16,-1).
%F G.f.: x*(1 + 4*x)/(1 - 16*x + x^2).
%F a(n) = -4*S(n, 16) + 65*S(n-1, 16) for n >= 1, with S(n,16) = A077412(n).
%F a(n) = sqrt((A307172(n)^2 - 9)/7) for n >= 1.
%Y Cf. A077421, A307168, A307169, A307172.
%K nonn,easy
%O 1,2
%A _Wolfdieter Lang_, Mar 28 2019
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