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 A006443 M1277 #34 Jan 20 2025 20:24:47 %S A006443 1,2,4,14,47,184,761,3314,14997,69886,333884,1626998,8067786,40580084, %T A006443 206734083,1064666724,5536480877,29036188788,153450351924, %U A006443 816503772830,4371551433888 %N A006443 Number of achiral planar maps with n edges. %C A006443 An achiral map is a map with a sense-reversing automorphism. %C A006443 The planar maps considered are connected and may contain loops and parallel edges. - _Andrew Howroyd_, Jan 13 2025 %D A006443 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006443 V. A. Liskovets, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/LISK/Derseq.html">Some easily derivable sequences</a>, J. Integer Sequences, 3 (2000), #00.2.2. %H A006443 Timothy R. Walsh, <a href="/A007401/a007401.pdf">Number of sensed planar maps with n edges and m vertices</a>, p. 43. %H A006443 Nicholas C. Wormald, <a href="http://dx.doi.org/10.1016/0012-365X(81)90238-7">Counting unrooted planar maps</a>, Discrete Math. 36 (1981), no. 2, 205-225. %F A006443 a(n) = 2*A006385(n) - A006384(n). [Liskovets eq 3a] - _R. J. Mathar_, Oct 01 2011 %Y A006443 Column k=0 of A380234. %Y A006443 Cf. A006384 (sensed), A006385 (unsensed), A006444 (2-connected), A006445 (3-connected). %K A006443 nonn,nice,more %O A006443 0,2 %A A006443 _N. J. A. Sloane_ %E A006443 a(0)=1 prepended by _Andrew Howroyd_, Jan 13 2025 %E A006443 a(20) added by _Andrew Howroyd_, Jan 20 2025