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 A146883 #31 Jan 07 2024 15:58:36
%S A146883 6,36,186,936,4686,23436,117186,585936,2929686,14648436,73242186,
%T A146883 366210936,1831054686,9155273436,45776367186,228881835936,
%U A146883 1144409179686,5722045898436,28610229492186,143051147460936,715255737304686
%N A146883 a(n) = 6 * Sum_{m=0..n} 5^m.
%H A146883 G. C. Greubel, <a href="/A146883/b146883.txt">Table of n, a(n) for n = 0..1000</a>
%H A146883 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,-5).
%F A146883 a(n) = Sum_{m=0..n} 6*5^m.
%F A146883 a(n) = 3*(5^(n+1) - 1)/2. - _Emeric Deutsch_, Nov 02 2017
%F A146883 G.f.: 6/((1-z)*(1-5*z)). - _Robert Israel_, Nov 02 2017
%F A146883 a(n) = 6 * A003463(n+1). - _Alois P. Heinz_, Nov 03 2017
%F A146883 E.g.f.: (3/2)*(5*exp(5*x) - exp(x)). - _G. C. Greubel_, Oct 12 2022
%t A146883 a[n_]:= 6*Sum[5^m, {m,0,n}]; Table[a[n], {n,0,30}]
%t A146883 (* Second programs: *)
%t A146883 Array[3(5^(#+1) -1)/2 &, 21, 0] (* or *)
%t A146883 CoefficientList[Series[6/((1-x)(1-5x)), {x, 0, 20}], x] (* _Michael De Vlieger_, Nov 02 2017 *)
%t A146883 LinearRecurrence[{6,-5},{6,36},30] (* _Harvey P. Dale_, Jan 07 2024 *)
%o A146883 (PARI) a(n) = sum(m=0, n, 6*5^m); \\ _Michel Marcus_, Nov 03 2017
%o A146883 (Magma) [n le 2 select 6^n else 6*Self(n-1) -5*Self(n-2): n in [1..31]]; // _G. C. Greubel_, Oct 12 2022
%o A146883 (SageMath) [3*(5^(n+1) -1)/2 for n in range(41)] # _G. C. Greubel_, Oct 12 2022
%Y A146883 Cf. A003463, A100774.
%K A146883 nonn,easy,less
%O A146883 0,1
%A A146883 _Roger L. Bagula_, Nov 02 2008