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 | 1 |
| 2 | 5 |
| 3 | 26 |
| 4 | 154 |
| 5 | 1044 |
| 6 | 8028 |
| 7 | 69264 |
| 8 | 663696 |
| 9 | 6999840 |
| 10 | 80627040 |
| 11 | 1007441280 |
| 12 | 13575738240 |
| 13 | 196287356160 |
| 14 | 3031488633600 |
| 15 | 49811492505600 |
| 16 | 867718162483200 |
| 17 | 15974614352793600 |
| 18 | 309920046408806400 |
| 19 | 6320046028584960000 |
| 20 | 135153868608460800000 |
| 21 | 3024476051557847040000 |