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 | 1 |
| 2 | 14 |
| 3 | 148 |
| 4 | 1400 |
| 5 | 12496 |
| 6 | 107744 |
| 7 | 908608 |
| 8 | 7548800 |
| 9 | 62070016 |
| 10 | 506637824 |
| 11 | 4113568768 |
| 12 | 33271347200 |
| 13 | 268347559936 |
| 14 | 2159841173504 |
| 15 | 17357093552128 |
| 16 | 139326933401600 |
| 17 | 1117436577120256 |
| 18 | 8956419276406784 |
| 19 | 71752914167922688 |
| 20 | 574632673083392000 |
| 21 | 4600717543107198976 |