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 | 28 |
| 3 | 220 |
| 4 | 1820 |
| 5 | 15504 |
| 6 | 134596 |
| 7 | 1184040 |
| 8 | 10518300 |
| 9 | 94143280 |
| 10 | 847660528 |
| 11 | 7669339132 |
| 12 | 69668534468 |
| 13 | 635013559600 |
| 14 | 5804731963800 |
| 15 | 53194089192720 |
| 16 | 488526937079580 |
| 17 | 4495151581425648 |
| 18 | 41432089765583440 |
| 19 | 382460951663844400 |