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) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 4 |
| 6 | 9 |
| 7 | 32 |
| 8 | 90 |
| 9 | 240 |
| 10 | 654 |
| 11 | 1804 |
| 12 | 4950 |
| 13 | 13664 |
| 14 | 37944 |
| 15 | 106272 |
| 16 | 298890 |
| 17 | 843796 |
| 18 | 2390595 |
| 19 | 6796160 |
| 20 | 19370696 |
| 21 | 55345680 |
| 22 | 158489298 |
| 23 | 454803100 |
| 24 | 1307556162 |
| 25 | 3765741324 |
| 26 | 10862667648 |
| 27 | 31381058880 |
| 28 | 90780903460 |
| 29 | 262951527460 |