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 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 48 |
| 5 | 132 |
| 6 | 240 |
| 7 | 528 |
| 8 | 1364 |
| 9 | 4180 |
| 10 | 7560 |
| 11 | 20784 |
| 12 | 42768 |
| 13 | 70992 |
| 14 | 151632 |
| 15 | 446208 |
| 16 | 986880 |
| 17 | 1688400 |
| 18 | 4006800 |
| 19 | 6080256 |
| 20 | 13843440 |
| 21 | 42125380 |
| 22 | 79567488 |
| 23 | 152712000 |
| 24 | 292573440 |
| 25 | 526051328 |
| 26 | 797636448 |
| 27 | 2942476992 |
| 28 | 7257012896 |