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) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 20 |
| 5 | 86 |
| 6 | 424 |
| 7 | 2128 |
| 8 | 11200 |
| 9 | 60372 |
| 10 | 333254 |
| 11 | 1872728 |
| 12 | 10688284 |
| 13 | 61792756 |
| 14 | 361247006 |
| 15 | 2132290212 |
| 16 | 12692489494 |
| 17 | 76115308712 |
| 18 | 459476777038 |
| 19 | 2790092370660 |
| 20 | 17032567789840 |
| 21 | 104478722395496 |
| 22 | 643682329681246 |
| 23 | 3981493201581658 |