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 A274032 #39 Aug 03 2016 00:17:32 %S A274032 3,-9,83,-753,6851,-62329,567059,-5159009,46935811,-427014249, %T A274032 3884905043,-35344223825,321555905219,-2925462465753,26615373873171, %U A274032 -242142271419073,2202970354179075,-20042260085157577,182341168849178195,-1658909809373582257 %N A274032 Sum of n-th powers of the roots of x^3 + 9*x^2 - x - 1. %C A274032 A Berndt-type sequence for tan(2*Pi/7). %C A274032 a(n) is always an integer. %C A274032 a(n) is x1^n + x2^n + x3^n, where x1, x2, x3 are the roots of the polynomial %C A274032 x^3 + 9*x^2 - x - 1. %C A274032 x1 = tan(Pi/7)/tan(2*Pi/7), %C A274032 x2 = tan(2*Pi/7)/tan(4*Pi/7), %C A274032 x3 = tan(4*Pi/7)/tan(Pi/7). %C A274032 This is a two sided sequence. The other half is A274075. - _Kai Wang_, Aug 02 2016 %H A274032 Seiichi Manyama, <a href="/A274032/b274032.txt">Table of n, a(n) for n = 0..1000</a> %H A274032 B. C. Berndt, L.-C. Zhang, <a href="http://dx.doi.org/10.1007/BF01444636">Ramanujan's identities for eta-functions</a>, Math. Ann. 292 (1992), 561-573. %H A274032 Roman Witula, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL12/Witula/witula17.html">Ramanujan Type Trigonometric Formulas: The General Form for the Argument 2Pi/7</a>, J. Integer Seq., 12 (2009), Article 09.8.5. %H A274032 Roman Witula and Damian Slota, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL10/Slota/witula13.html">New Ramanujan-Type Formulas and Quasi-Fibonacci Numbers of Order 7</a>, Journal of Integer Sequences, Vol. 10 (2007), Article 07.5.6 %H A274032 Roman Witula and Damian Slota, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL10/Slota2/slota99.html">Quasi-Fibonacci Numbers of Order 11</a>, Journal of Integer Sequences, Vol. 10 (2007), Article 07.8.5 %H A274032 Roman Witula, Damian Slota and Adam Warzynski, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL9/Slota/slota57.html">Quasi-Fibonacci Numbers of the Seventh Order</a>, J. Integer Seq., 9 (2006), Article 06.4.3. %H A274032 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-9,1,1). %F A274032 a(n) = (tan(Pi/7)/tan(2*Pi/7))^n + (-tan(2*Pi/7)/tan(3*Pi/7))^n + (-tan(3*Pi/7)/tan(Pi/7))^n. %F A274032 From _Colin Barker_, Jun 07 2016: (Start) %F A274032 a(n) = -9*a(n-1)+a(n-2)+a(n-3) for n>2. %F A274032 G.f.: (3+18*x-x^2) / (1+9*x-x^2-x^3). %F A274032 (End) %o A274032 (PARI) Vec((3+18*x-x^2)/(1+9*x-x^2-x^3) + O(x^30)) \\ _Colin Barker_, Jun 07 2016 %o A274032 (PARI) polsym(x^3 + 9*x^2 - x - 1, 30) \\ _Charles R Greathouse IV_, Jul 20 2016 %Y A274032 Cf. A033304, A094648, A215076, A274075. %K A274032 sign,easy %O A274032 0,1 %A A274032 _Kai Wang_, Jun 07 2016 %E A274032 Edited by _N. J. A. Sloane_, Jun 07 2016