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 A130215 #15 Jan 17 2024 09:06:46
%S A130215 0,168,58800,20176632,6920642400,2373780746568,814206798896400,
%T A130215 279272932041230232,95790615690280324800,32856181181767119892968,
%U A130215 11269670145346128902694000,3865496859853722261079883832,1325865422929826735882591047200,454771840064930570410054065439368
%N A130215 Order of modular group of degree 7^(n-1)+1.
%D A130215 E. Mathieu, Mémoire sur le nombre de valeurs que peut acquérir une fonction quand on y permute ses variables de toutes les manières possibles, Journ. de math. (2) 5 (1860), 9-42 (see p. 39).
%H A130215 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (350,-2401).
%F A130215 a(n) = (7^(n-1))*(7^(2n-2)-1)/2.
%F A130215 a(n) = 350*a(n-1)-2401*a(n-2). G.f.: 168*x^2 / ((7*x-1)*(343*x-1)). - _Colin Barker_, Sep 02 2013
%t A130215 Table[7^(x - 1) (7^(2 x - 2) - 1)/2, {x, 1, 15}]
%t A130215 LinearRecurrence[{350,-2401},{0,168},20] (* _Harvey P. Dale_, Aug 01 2022 *)
%Y A130215 Cf. A120689.
%K A130215 nonn,easy
%O A130215 1,2
%A A130215 _Artur Jasinski_, Aug 04 2007
%E A130215 More terms from _Colin Barker_, Sep 02 2013