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 | 2 |
| 3 | 2 |
| 4 | -4 |
| 5 | -16 |
| 6 | 0 |
| 7 | 96 |
| 8 | 192 |
| 9 | -384 |
| 10 | -3840 |
| 11 | -3840 |
| 12 | 69120 |
| 13 | 184320 |
| 14 | -1290240 |
| 15 | -5160960 |
| 16 | 25804800 |
| 17 | 134184960 |
| 18 | -557383680 |
| 19 | -3530096640 |
| 20 | 13005619200 |
| 21 | 96613171200 |
| 22 | -326998425600 |
| 23 | -2779486617600 |
| 24 | 8828957491200 |
| 25 | 84365593804800 |
| 26 | -255058771968000 |
| 27 | -2703622982860800 |
| 28 | 7855810176614400 |