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 | 3 |
| 3 | 20 |
| 4 | 148 |
| 5 | 1384 |
| 6 | 15728 |
| 7 | 207696 |
| 8 | 3094152 |
| 9 | 51423288 |
| 10 | 945943512 |
| 11 | 19083180192 |
| 12 | 418550811600 |
| 13 | 9907493349168 |
| 14 | 251588827187280 |
| 15 | 6820899616891008 |
| 16 | 196645361557479552 |
| 17 | 6007407711127690752 |
| 18 | 193842462200078260224 |
| 19 | 6586904673329133618432 |
| 20 | 235079477736802622742528 |
| 21 | 8790132360155070084076800 |