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 A100058 #17 Feb 06 2025 23:45:11
%S A100058 1,3,10,31,97,302,941,2931,9130,28439,88585,275934,859509,2677291,
%T A100058 8339514,25976815,80915377,252043918,785093501,2445493667,7617486666,
%U A100058 23727766663,73909799321,230222191294,717120839877,2233765112283
%N A100058 Expansion of 1 / (1 - 3x - x^2 + 2x^3).
%C A100058 a(n)/a(n-1) tends to 3.1149075414..., which is an eigenvalue of the matrix M and a root of the characteristic polynomial x^3 - 3x^2 - x + 2.
%D A100058 Boris A. Bondarenko, Generalized Pascal Triangles and Pyramids (in Russian), FAN, Tashkent, 1990, ISBN 5-648-00738-8.
%H A100058 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3, 1, -2).
%H A100058 Boris A. Bondarenko, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/pascal.html">Generalized Pascal Triangles and Pyramids</a>, English translation published by Fibonacci Association, Santa Clara Univ., Santa Clara, CA, 1993; see p. 27.
%F A100058 Recurrence: a(0) = 1, a(1) = 3, a(2) = 10; a(n) = 3*a(n-1) + a(n-2) - 2*a(n-3).
%F A100058 Given Hosoya's triangle: 1; 1, 1; 2, 1, 2; considered as an upper triangular 3 X 3 matrix M: [2 1 2 / 1 1 0 / 1 0 0]; a(n) = center term in M^n * [1 0 0].
%e A100058 a(5) = 97, center term in M^5 * [1 0 0]: [205 97 66].
%t A100058 CoefficientList[Series[1/(1 - 3x - x^2 + 2x^3), {x, 0, 25}], x] (* Or *)
%t A100058 Table[(MatrixPower[{{2, 1, 2}, {1, 1, 0}, {1, 0, 0}}, n].{1, 0, 0})[[2]], {n, 26}] (* _Robert G. Wilson v_, Nov 04 2004 *)
%t A100058 LinearRecurrence[{3,1,-2},{1,3,10},30] (* _Harvey P. Dale_, Mar 28 2012 *)
%o A100058 (PARI) Vec(1/(1-3*x-x^2+2*x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%Y A100058 Partial sums of A052911. Cf. A019481, A052550, A052939, A100059, A058071.
%K A100058 nonn,easy
%O A100058 0,2
%A A100058 _Gary W. Adamson_, Oct 31 2004
%E A100058 Edited by _Ralf Stephan_, Nov 02 2004
%E A100058 Corrected and extended by _Robert G. Wilson v_, Nov 04 2004