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 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 20 |
| 5 | 252 |
| 6 | 6435 |
| 7 | 352716 |
| 8 | 40116600 |
| 9 | 9075135300 |
| 10 | 4116715363800 |
| 11 | 3824345300380220 |
| 12 | 7219428434016265740 |
| 13 | 27217014869199032015600 |
| 14 | 205397724721029574666088520 |
| 15 | 3136262529306125724764953838760 |