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 | 4 |
| 2 | 12 |
| 3 | 60 |
| 4 | 364 |
| 5 | 2448 |
| 6 | 17556 |
| 7 | 131560 |
| 8 | 1017900 |
| 9 | 8069424 |
| 10 | 65204656 |
| 11 | 535070172 |
| 12 | 4446927732 |
| 13 | 37353738800 |
| 14 | 316621743480 |
| 15 | 2704784196240 |
| 16 | 23263187479980 |
| 17 | 201275443944432 |
| 18 | 1750651680235920 |
| 19 | 15298438066553776 |
| 20 | 134252511729576240 |
| 21 | 1182622941581590080 |