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 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 52 |
| 5 | 450 |
| 6 | 3410 |
| 7 | 41748 |
| 8 | 415952 |
| 9 | 5985144 |
| 10 | 79468648 |
| 11 | 1263309960 |
| 12 | 20581146056 |
| 13 | 375092849040 |
| 14 | 7053697259856 |
| 15 | 144054799315560 |
| 16 | 3108398855786496 |
| 17 | 70281839877041088 |
| 18 | 1687564595412611520 |
| 19 | 42264952015652902656 |
| 20 | 1114043035100431983744 |
| 21 | 30552235678578565203840 |