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 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 48 |
| 5 | 315 |
| 6 | 2497 |
| 7 | 23394 |
| 8 | 254132 |
| 9 | 3149826 |
| 10 | 43945354 |
| 11 | 682314028 |
| 12 | 11676044036 |
| 13 | 218402171520 |
| 14 | 4433885571840 |
| 15 | 97098961376112 |
| 16 | 2281563329170752 |
| 17 | 57255174735315792 |
| 18 | 1528204674443305680 |
| 19 | 43227315891291907488 |
| 20 | 1291646719998952196448 |
| 21 | 40652195494651491747840 |