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 | 0 |
| 4 | 0 |
| 5 | 120 |
| 6 | -1800 |
| 7 | 21000 |
| 8 | -235200 |
| 9 | 2693880 |
| 10 | -30504600 |
| 11 | 310239600 |
| 12 | -2026767600 |
| 13 | -22324267680 |
| 14 | 1480359360480 |
| 15 | -48314853350400 |
| 16 | 1332965821824000 |
| 17 | -34178451017685120 |
| 18 | 837433109548661760 |
| 19 | -19671723873906894720 |
| 20 | 436228097513559408000 |