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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 31 |
| 5 | 227 |
| 6 | 1782 |
| 7 | 15564 |
| 8 | 151455 |
| 9 | 1635703 |
| 10 | 19457998 |
| 11 | 252962528 |
| 12 | 3568119351 |
| 13 | 54262590843 |
| 14 | 884831668974 |
| 15 | 15397747311556 |
| 16 | 284767367151241 |
| 17 | 5576696534340377 |
| 18 | 115269731259650802 |
| 19 | 2507575460681918232 |
| 20 | 57262481202198407625 |
| 21 | 1369461739333488200365 |