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a(n) = ((2*n)^(2*n+2) - 1)/(4*n^2 - 1).
1

%I #16 Sep 08 2022 08:45:04

%S 1,5,273,47989,17043521,10101010101,8978450801041,11168991475945493,

%T 18519084246547628289,39468223580173616639125,

%U 105120401002506265664160401,342134767379466388778420319285,1336055317331762879448123353666113

%N a(n) = ((2*n)^(2*n+2) - 1)/(4*n^2 - 1).

%H Harry J. Smith, <a href="/A066210/b066210.txt">Table of n, a(n) for n = 0..100</a>

%t Table[((2n)^(2n+2)-1)/(4n^2-1),{n,0,20}] (* _Harvey P. Dale_, Jan 18 2020 *)

%o (PARI) { for (n=0, 100, write("b066210.txt", n, " ", ((2*n)^(2*n+2)-1)/(4*n^2-1)) ) } \\ _Harry J. Smith_, Feb 06 2010

%o (Magma) [((2*n)^(2*n+2) - 1)/(4*n^2 - 1): n in [0..12]]; // _Vincenzo Librandi_, Jan 19 2020

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Dec 17 2001