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.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 2 |
| 4 | 6 |
| 5 | 75 |
| 6 | 21 |
| 7 | 208 |
| 8 | 3950 |
| 9 | 540 |
| 10 | 11220 |
| 11 | 314880 |
| 12 | 25740 |
| 13 | 917280 |
| 14 | 36029700 |
| 15 | 1965600 |
| 16 | 107100000 |
| 17 | 5627890800 |
| 18 | 219769200 |
| 19 | 16995484800 |
| 20 | 1153034190000 |
| 21 | 33844456800 |
| 22 | 3525796058400 |
| 23 | 300234909744000 |
| 24 | 6868433880000 |
| 25 | 927359072640000 |
| 26 | 96883959332160000 |
| 27 | 1776393899280000 |
| 28 | 301733192320560000 |