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 | 0 |
| 1 | 3 |
| 2 | 21 |
| 3 | 990 |
| 4 | 6786 |
| 5 | 318801 |
| 6 | 2185095 |
| 7 | 102652956 |
| 8 | 703593828 |
| 9 | 33053933055 |
| 10 | 226555027545 |
| 11 | 10643263790778 |
| 12 | 72950015275686 |
| 13 | 3427097886697485 |
| 14 | 23489678363743371 |
| 15 | 1103514876252799416 |
| 16 | 7563603483110089800 |
| 17 | 355328363055514714491 |
| 18 | 2435456831883085172253 |
| 19 | 114414629388999485266710 |