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 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 14 |
| 6 | 38 |
| 7 | 216 |
| 8 | 600 |
| 9 | 6240 |
| 10 | 9552 |
| 11 | 319296 |
| 12 | -519312 |
| 13 | 28108560 |
| 14 | -176474352 |
| 15 | 3998454144 |
| 16 | -43985078784 |
| 17 | 837126163584 |
| 18 | -12437000028288 |
| 19 | 237195036797184 |
| 20 | -4235955315745536 |
| 21 | 85886259443020800 |
| 22 | -1746536474655406080 |
| 23 | 38320721602434017280 |
| 24 | -864056965711935974400 |