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 | 12 |
| 4 | 84 |
| 5 | 680 |
| 6 | 6750 |
| 7 | 78372 |
| 8 | 1035608 |
| 9 | 15402816 |
| 10 | 254672730 |
| 11 | 4631221100 |
| 12 | 91872810612 |
| 13 | 1974481960464 |
| 14 | 45698618329910 |
| 15 | 1133221107064620 |
| 16 | 29974735063385520 |
| 17 | 842413032202481792 |
| 18 | 25067919890384214066 |
| 19 | 787394937539847359052 |
| 20 | 26034146454319615550540 |