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 | 0 |
| 1 | 0 |
| 2 | 3 |
| 3 | 28 |
| 4 | 133 |
| 5 | 510 |
| 6 | 1790 |
| 7 | 5997 |
| 8 | 19639 |
| 9 | 63541 |
| 10 | 204037 |
| 11 | 652173 |
| 12 | 2078320 |
| 13 | 6609816 |
| 14 | 20993381 |
| 15 | 66612867 |
| 16 | 211222374 |
| 17 | 669428537 |
| 18 | 2120835892 |
| 19 | 6717184256 |
| 20 | 21270247404 |
| 21 | 67341572823 |
| 22 | 213173925948 |
| 23 | 674739560651 |
| 24 | 2135491756895 |
| 25 | 6758117426102 |
| 26 | 21385762133815 |
| 27 | 67670426242420 |