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 | 10 |
| 4 | 40 |
| 5 | 320 |
| 6 | 3200 |
| 7 | 35200 |
| 8 | 510400 |
| 9 | 11440000 |
| 10 | 205440000 |
| 11 | 3543320000 |
| 12 | 115310400000 |
| 13 | 2505522400000 |
| 14 | 104014341200000 |
| 15 | 2440423132000000 |
| 16 | 112255444052000000 |
| 17 | 3300252314304000000 |
| 18 | 143012413513200000000 |
| 19 | 5313433311353200000000 |
| 20 | 302523154413030400000000 |