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 A308750 #11 Jun 24 2019 04:38:09 %S A308750 1,1,2,7,36,239,1892,17015,168503,1799272,20409644 %N A308750 Number of Dumont permutations of the first kind of length 2n avoiding pattern 2143 (or pattern 3421). %C A308750 Conjecture: The number of Dumont permutations of the first kind avoiding pattern 2143 equals the number of Dumont permutations of the first kind avoiding pattern 3421 for all n >= 0. %C A308750 Data for n=7,8,9,10 is due to _Michael Albert_. %D A308750 O. Jones, Enumeration of Dumont permutations avoiding certain four-letter patterns, Ph.D. thesis, Howard University, 2019. %H A308750 D. Dumont, <a href="http://dx.doi.org/10.1215/S0012-7094-74-04134-9">Interprétations combinatoires des nombres de Genocchi</a>, Duke Math. J., 41 (1974), 305-318. %e A308750 For n=3, the 7 Dumont permutations of the first kind avoiding pattern 2143 are 356421, 364215, 435621, 563421, 564213, 634215, 642135, and the 7 Dumont permutations of the first kind avoiding pattern 3421 are 214365, 216435, 421365, 421563, 421635, 621435, 642135. %Y A308750 Cf. A001469, A110501. %K A308750 nonn,more %O A308750 0,3 %A A308750 _Alexander Burstein_ and _Opel Jones_, Jun 21 2019