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 | 6 |
| 3 | 30 |
| 4 | 126 |
| 5 | 1565 |
| 6 | 8190 |
| 7 | 131070 |
| 8 | 524286 |
| 9 | 7511964 |
| 10 | 89777599 |
| 11 | 2147483646 |
| 12 | 20166585982 |
| 13 | 840455563322 |
| 14 | 4787976306682 |
| 15 | 5519162753736 |
| 16 | 2617809209727498 |
| 17 | 334169564069012755 |
| 18 | 2305843009213693950 |
| 19 | 47306781863857413639 |