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 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 150 |
| 6 | 534 |
| 7 | 1806 |
| 8 | 5760 |
| 9 | 18144 |
| 10 | 55830 |
| 11 | 171006 |
| 12 | 518580 |
| 13 | 1569750 |
| 14 | 4732014 |
| 15 | 14250450 |
| 16 | 42844320 |
| 17 | 128746950 |
| 18 | 386615376 |
| 19 | 1160688606 |
| 20 | 3483582660 |
| 21 | 10454059938 |
| 22 | 31368305694 |
| 23 | 94118013006 |
| 24 | 282378679920 |
| 25 | 847187946000 |
| 26 | 2541662931990 |
| 27 | 7625194813656 |
| 28 | 22875982414740 |