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 | 30 |
| 4 | 284 |
| 5 | 3240 |
| 6 | 43282 |
| 7 | 662760 |
| 8 | 11446844 |
| 9 | 220193310 |
| 10 | 4669558564 |
| 11 | 108251161920 |
| 12 | 2723857695362 |
| 13 | 73941952968000 |
| 14 | 2154117314613604 |
| 15 | 67038931862069790 |
| 16 | 2219781607638887804 |
| 17 | 77922680046440538600 |
| 18 | 2890682855602209593362 |
| 19 | 112998995448368143038120 |
| 20 | 4642614436461699746566364 |