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 A130213 #17 Mar 09 2021 04:15:46
%S A130213 0,12,360,9828,265680,7174332,193709880,5230175508,141214764960,
%T A130213 3812798732652,102945566017800,2779530283189188,75047317648233840,
%U A130213 2026277576508690972,54709494565753788120,1477156353275409674868,39883221538436233408320,1076846981537778818585292
%N A130213 Order of modular group of degree 3^(n-1) + 1.
%D A130213 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 A130213 Ronald P. Nordgren, <a href="https://arxiv.org/abs/2103.04774">Compound Lucas Magic Squares</a>, arXiv:2103.04774 [math.GM], 2021. See Table 2 p. 12.
%H A130213 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (30,-81).
%F A130213 a(n) = 3^(n-1)*(3^(2*n - 2) - 1)/2.
%F A130213 From _Colin Barker_, Sep 02 2013: (Start)
%F A130213 a(n) = 30*a(n-1) - 81*a(n-2).
%F A130213 G.f.: 12*x^2 / ((3*x-1)*(27*x-1)). (End)
%t A130213 Table[3^(x - 1) (3^(2 x - 2) - 1)/2, {x, 1, 15}]
%Y A130213 Cf. A120689.
%K A130213 nonn,easy
%O A130213 1,2
%A A130213 _Artur Jasinski_, Aug 04 2007
%E A130213 More terms from _Colin Barker_, Sep 02 2013