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 | 1 |
| 3 | 4 |
| 4 | 19 |
| 5 | 116 |
| 6 | 835 |
| 7 | 6890 |
| 8 | 63826 |
| 9 | 654552 |
| 10 | 7354893 |
| 11 | 89830770 |
| 12 | 1184915556 |
| 13 | 16788863356 |
| 14 | 254342837905 |
| 15 | 4103256660048 |
| 16 | 70241858430220 |
| 17 | 1271839899568064 |
| 18 | 24287699718766932 |
| 19 | 487891841580468294 |
| 20 | 10285169201486942788 |
| 21 | 227042177973572054900 |