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 A083222 #21 Sep 08 2022 08:45:10
%S A083222 1,3,25,75,625,1875,15625,46875,390625,1171875,9765625,29296875,
%T A083222 244140625,732421875,6103515625,18310546875,152587890625,457763671875,
%U A083222 3814697265625,11444091796875,95367431640625,286102294921875
%N A083222 a(n) = (4*5^n + (-5)^n)/5.
%C A083222 Binomial transform of A083297.
%H A083222 Vincenzo Librandi, <a href="/A083222/b083222.txt">Table of n, a(n) for n = 0..300</a>
%H A083222 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,25).
%F A083222 a(n) = (4*5^n + (-5)^n)/5.
%F A083222 G.f.: (1+3*x)/((1+5*x)(1-5*x)).
%F A083222 E.g.f.: (4*exp(5*x) + exp(-5*x))/5.
%t A083222 LinearRecurrence[{0,25},{1,3},30] (* or *) Riffle[NestList[25#&,1,10], NestList[ 25#&,3,10]] (* _Harvey P. Dale_, Dec 14 2017 *)
%o A083222 (Magma) [(4*5^n+(-5)^n)/5: n in [0..25]]; // _Vincenzo Librandi_, Jun 29 2011
%o A083222 (PARI) a(n)=(4*5^n+(-5)^n)/5 \\ _Charles R Greathouse IV_, Jun 29 2011
%Y A083222 Cf. A083223, A083299.
%K A083222 easy,nonn
%O A083222 0,2
%A A083222 _Paul Barry_, Apr 23 2003
%E A083222 Edited by _N. J. A. Sloane_, Jun 08 2007