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 A096881 #28 Jan 01 2024 11:06:19
%S A096881 1,4,17,68,289,1156,4913,19652,83521,334084,1419857,5679428,24137569,
%T A096881 96550276,410338673,1641354692,6975757441,27903029764,118587876497,
%U A096881 474351505988,2015993900449,8063975601796,34271896307633,137087585230532,582622237229761,2330488948919044
%N A096881 Expansion of g.f. (1 + 4*x)/(1 - 17*x^2).
%H A096881 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,17).
%F A096881 a(n) = 3*a(n-1) + 4*a(n-2) + 17^floor((n-2)/2).
%F A096881 a(n) = Sum_{k=0..floor(n/2)} binomial(floor(n/2), k)*4^(n-2*k).
%F A096881 a(n) = 17*a(n-2), n>1. - _Harvey P. Dale_, Jan 21 2012
%F A096881 E.g.f.: cosh(sqrt(17)*x) + 4*sinh(sqrt(17)*x)/sqrt(17). - _Stefano Spezia_, Mar 31 2023
%t A096881 CoefficientList[Series[(1+4x)/(1-17x^2),{x,0,30}],x] (* or *) LinearRecurrence[ {0,17},{1,4},30] (* _Harvey P. Dale_, Jan 21 2012 *)
%o A096881 (PARI) Vec((1+4*x)/(1-17*x^2) + O(x^40)) \\ _Michel Marcus_, Jan 26 2016
%o A096881 (Magma) I:=[1,4,17]; [n le 3 select I[n] else 17*Self(n-2): n in [1..30]]; // _Vincenzo Librandi_, Jan 26 2016
%Y A096881 Cf. A004663, A026383, A016116.
%K A096881 easy,nonn
%O A096881 0,2
%A A096881 _Paul Barry_, Jul 14 2004
%E A096881 More terms from _Stefano Spezia_, Mar 31 2023