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 | 3 |
| 2 | 10 |
| 3 | 36 |
| 4 | 152 |
| 5 | 770 |
| 6 | 4632 |
| 7 | 32438 |
| 8 | 259520 |
| 9 | 2335698 |
| 10 | 23357000 |
| 11 | 256927022 |
| 12 | 3083124288 |
| 13 | 40080615770 |
| 14 | 561128620808 |
| 15 | 8416929312150 |
| 16 | 134670868994432 |
| 17 | 2289404772905378 |
| 18 | 41209285912296840 |
| 19 | 782976432333639998 |
| 20 | 15659528646672800000 |
| 21 | 328850101580128800042 |