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 A320499 #17 Jan 28 2020 03:41:40 %S A320499 1,1,0,1,3,14,62,572,7409,163284,5736443,342169618,33534945769, %T A320499 5442700283638,1484664946343496,664513607618098252, %U A320499 508538464299389501337,635542752091150346032474,1374528064543283977151585962,4842758246111267151697826493193 %N A320499 Number of connected self-dual signed graphs with n nodes. %H A320499 Edward A. Bender and E. Rodney Canfield, <a href="https://doi.org/10.1016/0095-8956(83)90040-0">Enumeration of connected invariant graphs</a>, Journal of Combinatorial Theory, Series B 34.3 (1983): 268-278. See p. 273, fourth table. %H A320499 Andrew Howroyd, <a href="/A320499/a320499.txt">PARI Program</a> %F A320499 a(2*n-1) = b(2*n-1), a(2*n) = b(2*n) - (A053465(n) - a(n))/2 where b is the Inverse Euler transform of A004104. - _Andrew Howroyd_, Jan 27 2020 %o A320499 (PARI) \\ See link for program. %o A320499 A320499seq(20) \\ _Andrew Howroyd_, Jan 27 2020 %Y A320499 Cf. A004102 (signed graphs), A004104 (self-dual), A053465 (connected signed graphs). %K A320499 nonn %O A320499 0,5 %A A320499 _N. J. A. Sloane_, Oct 26 2018 %E A320499 Dead sequence restored by _Andrew Howroyd_, Jan 26 2020 %E A320499 a(0)=1 prepended and terms a(13) and beyond from _Andrew Howroyd_, Jan 26 2020