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 | 4 |
| 2 | 18 |
| 3 | 104 |
| 4 | 671 |
| 5 | 4624 |
| 6 | 33342 |
| 7 | 248412 |
| 8 | 1897219 |
| 9 | 14774152 |
| 10 | 116864936 |
| 11 | 936390692 |
| 12 | 7584216152 |
| 13 | 61992689940 |
| 14 | 510728310716 |
| 15 | 4236545121924 |
| 16 | 35354229533389 |
| 17 | 296604036437692 |
| 18 | 2500154435955614 |
| 19 | 21164005790766980 |
| 20 | 179841032283906149 |
| 21 | 1533499916749203208 |