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 | 4 |
| 2 | 21 |
| 3 | 123 |
| 4 | 757 |
| 5 | 4788 |
| 6 | 30817 |
| 7 | 200784 |
| 8 | 1320093 |
| 9 | 8740284 |
| 10 | 58193673 |
| 11 | 389233287 |
| 12 | 2613338091 |
| 13 | 17602627006 |
| 14 | 118892784555 |
| 15 | 804951501469 |
| 16 | 5461228061541 |
| 17 | 37120212399708 |
| 18 | 252720891884473 |
| 19 | 1723088114793535 |
| 20 | 11763751150648785 |