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 A154575 2n^2+12n+4. 1

%I

%S 18,36,58,84,114,148,186,228,274,324,378,436,498,564,634,708,786,868,

%T 954,1044,1138,1236,1338,1444,1554,1668,1786,1908,2034,2164,2298,2436,

%U 2578,2724,2874,3028,3186,3348,3514,3684,3858,4036,4218,4404,4594,4788

%N 2n^2+12n+4.

%C Sixth diagonal of A144562; 2*a(n)+28 is a square.

%H Vincenzo Librandi, <a href="/A154575/b154575.txt">Table of n, a(n) for n = 1..1000</a>

%H <a href="/index/Rea#recLCC">Index to sequences with linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F a(n)= 2*A028881(n+3). - R. J. Mathar, Jan 05 2011

%F G.f. -2*x*(2*x-3)*(x-3) / (x-1)^3 . - R. J. Mathar, Jan 05 2011

%F a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). - Vincenzo Librandi, Feb 26 2012

%t LinearRecurrence[{3, -3, 1}, {18, 36, 58}, 50] (* Vincenzo Librandi, Feb 26 2012

%o (MAGMA) I:=[18, 36, 58]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 26 2012

%o (PARI) for(n=1, 50, print1(2*n^2+12*n+4", ")); \\ Vincenzo Librandi, Feb 26 2012

%Y Cf. A144562, A153238, A067076.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Jan 12 2009

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