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 | 21 |
| 4 | 126 |
| 5 | 818 |
| 6 | 5594 |
| 7 | 39693 |
| 8 | 289510 |
| 9 | 2157150 |
| 10 | 16348960 |
| 11 | 125642146 |
| 12 | 976789620 |
| 13 | 7668465964 |
| 14 | 60708178054 |
| 15 | 484093913917 |
| 16 | 3884724864390 |
| 17 | 31348290348086 |
| 18 | 254225828706248 |
| 19 | 2070856216759478 |
| 20 | 16936016649259364 |