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 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 13 |
| 7 | 39 |
| 8 | 117 |
| 9 | 351 |
| 10 | 1054 |
| 11 | 3163 |
| 12 | 9490 |
| 13 | 28470 |
| 14 | 85410 |
| 15 | 256230 |
| 16 | 768691 |
| 17 | 2306074 |
| 18 | 6918223 |
| 19 | 20754669 |
| 20 | 62264007 |
| 21 | 186792021 |
| 22 | 560376064 |
| 23 | 1681128193 |
| 24 | 5043384580 |
| 25 | 15130153740 |
| 26 | 45390461220 |
| 27 | 136171383660 |