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 A059420 #13 May 11 2025 09:14:40 %S A059420 1,20,616,28160,1805056,154918400,17171485696,2389096202240, %T A059420 407776690241536,83793407533383680,20407552701432856576, %U A059420 5813146553630295326720,1914890082050142493474816,722310365729129175040655360,309331648183856602708764000256 %N A059420 A diagonal of A059419. %D A059420 L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 259. %F A059420 a(n) = A059419(2*n+3, 3). From the expansion of tan(x)^3/6. %o A059420 (PARI) a059419(n, k) = n!*polcoef(tan(x+x*O(x^n))^k/k!, n); %o A059420 a(n) = a059419(2*n+3, 3); \\ _Seiichi Manyama_, May 11 2025 %Y A059420 Cf. A059419, A060056, A060057. %K A059420 nonn,easy %O A059420 0,2 %A A059420 _N. J. A. Sloane_, Jan 30 2001 %E A059420 More terms from Larry Reeves (larryr(AT)acm.org), Feb 08 2001. Corrected and extended by _Wolfdieter Lang_, Feb 09 2001. %E A059420 Offset changed to 0 by _Seiichi Manyama_, May 11 2025