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) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 15 |
| 5 | 84 |
| 6 | 420 |
| 7 | 1980 |
| 8 | 9009 |
| 9 | 40040 |
| 10 | 175032 |
| 11 | 755820 |
| 12 | 3233230 |
| 13 | 13728792 |
| 14 | 57946200 |
| 15 | 243374040 |
| 16 | 1017958725 |
| 17 | 4242920400 |
| 18 | 17631691440 |
| 19 | 73078721100 |
| 20 | 302202005490 |
| 21 | 1247182879800 |
| 22 | 5137916074200 |
| 23 | 21132472200840 |
| 24 | 86794082253450 |
| 25 | 356013544661424 |
| 26 | 1458583920435600 |
| 27 | 5969389748449400 |