This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A006668 #24 Jul 08 2025 00:46:17
%S A006668 0,0,1,6,32,160,784,3808,18432,89088,430336,2078208,10035200,48455680,
%T A006668 233967616,1129701376,5454692352,26337607680,127169265664,
%U A006668 614027624448,2964787822592,14315262312448,69120201588736
%N A006668 Exponential self-convolution of Pell numbers (divided by 2).
%C A006668 Binomial transform of A084150. - _Paul Barry_, May 16 2003
%H A006668 Vincenzo Librandi, <a href="/A006668/b006668.txt">Table of n, a(n) for n = 0..1000</a>
%H A006668 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (6,-4,-8).
%F A006668 a(n) = ((2+sqrt(8))^n+(2-sqrt(8))^n-2^(n+1))/16; E.g.f. : exp(2x)(sinh(sqrt(2)x))^2/4=(exp(x)sinh(sqrt(2)x)/sqrt(2))^2/2. - _Paul Barry_, May 16 2003
%F A006668 G.f.: x^2/((1-2*x)*(1-4*x-4*x^2)). - _Bruno Berselli_, Aug 20 2011
%F A006668 a(n) = A006646(n)/2 = 2^(n-4)*(A002203(n) - 2). - _Vladimir Reshetnikov_, Oct 07 2016
%t A006668 LinearRecurrence[{6,-4,-8},{0,0,1},30] (* _Harvey P. Dale_, Jul 15 2014 *)
%t A006668 Table[2^(n-4)*(LucasL[n, 2] - 2), {n, 0, 20}] (* _Vladimir Reshetnikov_, Oct 07 2016 *)
%o A006668 (Magma) [Floor(((2+Sqrt(8))^n+(2-Sqrt(8))^n-2^(n+1))/16): n in [0..30] ]; // _Vincenzo Librandi_, Aug 20 2011
%Y A006668 Cf. A006646, A002203.
%K A006668 nonn,easy
%O A006668 0,4
%A A006668 _N. J. A. Sloane_