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 | 9 |
| 6 | -22 |
| 7 | 55 |
| 8 | -142 |
| 9 | 375 |
| 10 | -1009 |
| 11 | 2753 |
| 12 | -7599 |
| 13 | 21178 |
| 14 | -59509 |
| 15 | 168401 |
| 16 | -479477 |
| 17 | 1372536 |
| 18 | -3947678 |
| 19 | 11402376 |
| 20 | -33059314 |
| 21 | 96177750 |
| 22 | -280671373 |
| 23 | 821379083 |
| 24 | -2409938978 |
| 25 | 7087502564 |
| 26 | -20889306810 |
| 27 | 61691675424 |
| 28 | -182531101523 |
| 29 | 541000651928 |
| 30 | -1606046079955 |
| 31 | 4774977156350 |