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 | 3 |
| 3 | 16 |
| 4 | 126 |
| 5 | 1296 |
| 6 | 16071 |
| 7 | 228514 |
| 8 | 3607890 |
| 9 | 61891050 |
| 10 | 1135871490 |
| 11 | 22049362440 |
| 12 | 448790912004 |
| 13 | 9512960347260 |
| 14 | 208858963314735 |
| 15 | 4728736078065810 |
| 16 | 110006925920592810 |
| 17 | 2621619942885055530 |
| 18 | 63840054782606886630 |
| 19 | 1585094577104979776880 |
| 20 | 40054740803371374834780 |
| 21 | 1028483346608802276173280 |