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 A008989 #68 Mar 30 2024 12:17:55 %S A008989 1,1,2,6,19,76,376,2194,14614,106421,823832,6657811,55557329, %T A008989 475475046,4155030702,36959470662,333860366236 %N A008989 Number of immersions of an unoriented circle into the unoriented sphere with n double points. %D A008989 V. I. Arnold, Topological Invariants of Plane Curves and Caustics, American Math. Soc., 1994, p. 18. %H A008989 J. Cantarella, H. Chapman, and M. Mastin, <a href="https://arxiv.org/abs/1512.05749">Knot Probabilities in Random Diagrams</a>, arXiv preprint arXiv:1512.05749 [math.GT], 2015. Also Journal of Physics A: Mathematical and Theoretical, Vol. 49, No. 40 (2016), DOI: 10.1088/1751-8113/49/40/405001 %H A008989 R. Coquereaux and J.-B. Zuber, <a href="http://arxiv.org/abs/1507.03163">Maps, immersions and permutations</a>, arXiv preprint arXiv:1507.03163 [math.CO], 2015-2016. Also J. Knot Theory Ramifications 25, 1650047 (2016), <a href="http://dx.doi.org/10.1142/S0218216516500474">10.1142/S0218216516500474</a>. %H A008989 Guy Valette, <a href="https://doi.org/10.1007/s40598-016-0049-3">A Classification of Spherical Curves Based on Gauss Diagrams</a>, Arnold Math J. (2016) 2:383-405. %e A008989 G.f. = 1 + x + 2*x^2 + 6*x^3 + 19*x^4 + 76*x^5 + 376*x^6 + 2194*x^7 + ... %o A008989 (Magma) // see A260914 %Y A008989 Cf. A008986, A008987, A008988, A264759, A277739. First line of triangle A260914. %K A008989 nonn,more %O A008989 0,3 %A A008989 _N. J. A. Sloane_ %E A008989 a(6)-a(7) from _Guy Valette_, Feb 09 2004 %E A008989 a(8)-a(9) from _Robert Coquereaux_ and Jean-Bernard Zuber, Jul 21 2015 %E A008989 a(10) from same source added by _N. J. A. Sloane_, Mar 03 2016 %E A008989 a(11)-a(14) from _Brendan McKay_, Mar 11 2023 %E A008989 a(15)-a(16) from _Brendan McKay_, Mar 29 2024