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 | 0 |
| 4 | 6 |
| 5 | 48 |
| 6 | 260 |
| 7 | 1200 |
| 8 | 5106 |
| 9 | 20720 |
| 10 | 81876 |
| 11 | 318000 |
| 12 | 1223136 |
| 13 | 4675440 |
| 14 | 17815020 |
| 15 | 67769552 |
| 16 | 257700906 |
| 17 | 980240880 |
| 18 | 3731753180 |
| 19 | 14222737200 |
| 20 | 54278580036 |
| 21 | 207438938000 |
| 22 | 793940475900 |
| 23 | 3043140078000 |
| 24 | 11681057249536 |
| 25 | 44900438149296 |
| 26 | 172824331826580 |
| 27 | 666070256489680 |