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 | 0 |
| 2 | 2 |
| 3 | 3 |
| 4 | 44 |
| 5 | 90 |
| 6 | 2034 |
| 7 | 9240 |
| 8 | 168944 |
| 9 | 951048 |
| 10 | 24042600 |
| 11 | 185387400 |
| 12 | 4411634952 |
| 13 | 44020650960 |
| 14 | 1166597641104 |
| 15 | 14101322278680 |
| 16 | 399099955203840 |
| 17 | 5522583764698560 |
| 18 | 169123038510919104 |
| 19 | 2779010889700890240 |
| 20 | 87888034148774728320 |
| 21 | 1637061268780618450560 |