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 | 7 |
| 4 | 67 |
| 5 | 121 |
| 6 | 4551 |
| 7 | 5041 |
| 8 | 405371 |
| 9 | 888721 |
| 10 | 65326213 |
| 11 | 39916801 |
| 12 | 27854708575 |
| 13 | 6227020801 |
| 14 | 5417436748153 |
| 15 | 6968620334677 |
| 16 | 2744261072866171 |
| 17 | 355687428096001 |
| 18 | 2984245819328278077 |
| 19 | 121645100408832001 |
| 20 | 1177257398964663961517 |
| 21 | 545405274481512519361 |