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 | 4 |
| 3 | 19 |
| 4 | 132 |
| 5 | 1119 |
| 6 | 12057 |
| 7 | 151560 |
| 8 | 2234970 |
| 9 | 37355130 |
| 10 | 702161460 |
| 11 | 14608747440 |
| 12 | 333760916475 |
| 13 | 8297318063475 |
| 14 | 223043540630400 |
| 15 | 6444290305953675 |
| 16 | 199158606533605950 |
| 17 | 6554872218153191625 |
| 18 | 228899544451085017125 |
| 19 | 8452452568601816775000 |
| 20 | 329069272855540304587500 |