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 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 44 |
| 5 | 244 |
| 6 | 1744 |
| 7 | 13768 |
| 8 | 127952 |
| 9 | 1270736 |
| 10 | 14384096 |
| 11 | 172799296 |
| 12 | 2306400832 |
| 13 | 32442943168 |
| 14 | 498547591424 |
| 15 | 8031916728704 |
| 16 | 139611091407104 |
| 17 | 2533449773986048 |
| 18 | 49133884886866432 |
| 19 | 991341134236389376 |
| 20 | 21218511171980205056 |
| 21 | 471083434031674336256 |