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 A003431 M4857 #39 Jul 10 2022 14:58:33 %S A003431 1,1,0,0,1,12,104,956,10037,126578,1971005,38569954,958347642, %T A003431 30400603560,1234260982770,64187360439352,4275470549123119 %N A003431 Number of isomorphism classes of connected irreducible posets with n labeled points. %D A003431 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A003431 S. R. Finch, <a href="http://www.people.fas.harvard.edu/~sfinch/">Series-parallel networks</a> %H A003431 S. R. Finch, <a href="/A000084/a000084_2.pdf">Series-parallel networks</a>, July 7, 2003. [Cached copy, with permission of the author] %H A003431 R. P. Stanley, <a href="http://dx.doi.org/10.1090/S0002-9939-1974-0351928-7">Enumeration of posets generated by disjoint unions and ordinal sums</a>, Proc. Amer. Math. Soc. 45 (1974), 295-299. %H A003431 R. P. Stanley, <a href="/A003277/a003277.pdf">Letter to N. J. A. Sloane, c. 1991</a> %H A003431 J. A. Wright, <a href="/A000798/a000798_4.pdf">Letter to N. J. A. Sloane, Apr 06 1972, listing 18 sequences</a> %H A003431 <a href="/index/Pos#posets">Index entries for sequences related to posets</a> %Y A003431 Cf. A003430, A046906. %K A003431 nonn,nice,more %O A003431 0,6 %A A003431 _N. J. A. Sloane_ and _Richard Stanley_ %E A003431 More terms from _Richard Stanley_, Jun 19 2003 %E A003431 2 more terms from _Vladeta Jovovic_, Feb 17 2008 %E A003431 Title clarified by _Geoffrey Critzer_, Jul 08 2022 %E A003431 a(0) changed to 1 by _Geoffrey Critzer_, Jul 10 2022