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 A281581 #45 Jun 16 2025 16:26:43
%S A281581 1,4,21,127,807,5179,33111,210067,1321887,8255899,51225351,316067107,
%T A281581 1941032367,11873549419,72394874391,440204293747,2670669533247,
%U A281581 16172309991739,97779619272231,590423692897987,3561340764760527,21462312506478859
%N A281581 a(n) = (15*2^(2*n+2) + 15*2^(n+2) + 5*2^(n+3)*3^(n+1) - 24*5^(n+1))/120.
%H A281581 Seiichi Manyama, <a href="/A281581/b281581.txt">Table of n, a(n) for n = 0..1285</a>
%H A281581 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (17,-104,268,-240).
%F A281581 G.f.: ( 1-13*x+57*x^2-82*x^3 ) / ( (6*x-1)*(4*x-1)*(2*x-1)*(5*x-1) ). - _R. J. Mathar_, Mar 19 2017
%F A281581 a(n) = 6^n +2^(n-1)-5^n+4^n/2. - _R. J. Mathar_, Mar 19 2017
%t A281581 Table[(15*2^(2*n+2) + 15*2^(n+2) + 5*2^(n+3)*3^(n+1) - 24*5^(n+1)) / 120, {n, 0, 21}] (* _Indranil Ghosh_, Mar 05 2017 *)
%o A281581 (PARI)
%o A281581 a(n) = (15*2^(2*n+2) + 15*2^(n+2) + 5*2^(n+3)*3^(n+1) - 24*5^(n+1)) / 120;
%o A281581 for (n=0, 21, print1(a(n),", ")); \\ _Indranil Ghosh_, Mar 05 2017
%o A281581 (Python) def A281581(n): return (15*2**(2*n+2) + 15*2**(n+2) + 5*2**(n+3)*3**(n+1) - 24*5**(n+1)) / 120 # _Indranil Ghosh_, Mar 05 2017
%o A281581 (Ruby)
%o A281581 def A281581(n)
%o A281581 (0..n).map{|i| (15 * 2 ** (2 * i + 2) + 15 * 2 ** (i + 2) + 5 * 2 ** (i + 3) * 3 ** (i + 1) - 24 * 5 ** (i + 1)) / 120}
%o A281581 end
%Y A281581 Row n=5 of A283272.
%K A281581 nonn,easy
%O A281581 0,2
%A A281581 _Seiichi Manyama_, Mar 05 2017