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 A320469 #26 Aug 28 2019 11:52:43
%S A320469 1,1,13,49,277,1321,6733,33409,167557,836761,4185853,20925169,
%T A320469 104634037,523153801,2615801773,13078943329,65394847717,326973976441,
%U A320469 1634870406493,8174350983889,40871757016597,204358780888681,1021793912832013,5108969547382849,25544847770468677
%N A320469 a(n) = 3*a(n-1) + 10*a(n-2), n >= 2; a(0)=1, a(1)=1.
%H A320469 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,10).
%F A320469 a(n) = (4*(-2)^n + 3*5^n)/7.
%F A320469 G.f.: (1-2*x)/((1-5*x)*(1+2*x)).
%o A320469 (PARI) {a(n) = (4*(-2)^n+3*5^n)/7}
%o A320469 (PARI) N=40; x='x+O('x^N); Vec((1-2*x)/((1-5*x)*(1+2*x)))
%Y A320469 Cf. A053428, A224473 (trimorphic number), A320468, A321133.
%K A320469 nonn,easy
%O A320469 0,3
%A A320469 _Seiichi Manyama_, Aug 27 2019