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 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 150 |
| 6 | 540 |
| 7 | 1806 |
| 8 | 5796 |
| 9 | 18150 |
| 10 | 55980 |
| 11 | 171006 |
| 12 | 519156 |
| 13 | 1569750 |
| 14 | 4733820 |
| 15 | 14250606 |
| 16 | 42850116 |
| 17 | 128746950 |
| 18 | 386634060 |
| 19 | 1160688606 |
| 20 | 3483638676 |
| 21 | 10454061750 |
| 22 | 31368476700 |
| 23 | 94118013006 |
| 24 | 282379204836 |
| 25 | 847187946150 |
| 26 | 2541664501740 |
| 27 | 7625194831806 |