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 A181690 #22 Sep 24 2018 22:06:05 %S A181690 -1,-4,1,-11,6,-1,-26,23,-8,1,-57,72,-39,10,-1,-120,201,-150,59,-12,1, %T A181690 -247,522,-501,268,-83,14,-1,-502,1291,-1524,1037,-434,111,-16,1, %U A181690 -1013,3084,-4339,3598,-1905,656,-143,18,-1,-2036,7181,-11762,11535,-7408,3217,-942,179,-20,1 %N A181690 Riordan array T((1-x)^(-2) | 2x-1) read by rows. %C A181690 The first column is A000295 signed. - _Michel Marcus_, Feb 14 2014 %H A181690 Ana Luzón, <a href="http://arxiv.org/abs/0907.2328">Iterative Processes Related to Riordan Arrays: The Reciprocation and the Inversion of Power Series</a>, arXiv:0907.2328 [math.CO], 2009-2010; Discrete Math., 310 (2010), 3607-3618. %H A181690 Ana Luzón and Manuel A. Morón, <a href="http://dx.doi.org/10.1016/j.laa.2008.12.001">Riordan matrices in the reciprocation of quadratic polynomials</a>, Linear Algebra Appl. 430 (2009), no. 8-9, 22542270. %e A181690 Array begins: %e A181690 -1; %e A181690 -4, 1; %e A181690 -11, 6, -1; %e A181690 -26, 23, -8, 1; %e A181690 -57, 72, -39, 10, -1; %e A181690 -120, 201, -150, 59, -12, 1; %e A181690 ... %t A181690 t[n_, k_] := t[n, k] = If[n<0, 0, If[k==0, n+3-2^(n+2), If[k>n, 0, 2 t[n-1, k] - t[n-1, k-1]]]]; %t A181690 Table[t[n, k], {n, 0, 9}, {k, 0, n}] // Flatten (* _Jean-François Alcover_, Sep 24 2018, from PARI *) %o A181690 (PARI) t(n, k) = if (n < 0, 0, if (k == 0, n + 3 - 2^(n+2), if (k >n, 0, 2*tr(n-1, k) - tr(n-1, k-1)))); \\ _Michel Marcus_, Feb 14 2014 %Y A181690 Cf. A000295, A159856. %K A181690 sign,tabl %O A181690 0,2 %A A181690 _N. J. A. Sloane_, Nov 17 2010 %E A181690 a(0) corrected and more terms from _Michel Marcus_, Feb 14 2014