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 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 4969 |
| 8 | 39184 |
| 9 | 347544 |
| 10 | 3424320 |
| 11 | 37150741 |
| 12 | 439774085 |
| 13 | 5639099103 |
| 14 | 77873192126 |
| 15 | 1152123776419 |
| 16 | 18181366630226 |
| 17 | 304851804959519 |
| 18 | 5412206888619242 |
| 19 | 101424438933572112 |
| 20 | 2000731009697485843 |
| 21 | 41440364401733715980 |
| 22 | 899211137893661967405 |