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 | 4 |
| 3 | -9 |
| 4 | 24 |
| 5 | -60 |
| 6 | 154 |
| 7 | -391 |
| 8 | 997 |
| 9 | -2538 |
| 10 | 6465 |
| 11 | -16464 |
| 12 | 41932 |
| 13 | -106792 |
| 14 | 271981 |
| 15 | -692685 |
| 16 | 1764144 |
| 17 | -4492953 |
| 18 | 11442736 |
| 19 | -29142568 |
| 20 | 74220826 |
| 21 | -189026955 |
| 22 | 481417305 |
| 23 | -1226082390 |
| 24 | 3122609041 |
| 25 | -7952717776 |
| 26 | 20254126984 |
| 27 | -51583580784 |
| 28 | 131374006329 |
| 29 | -334585720425 |
| 30 | 852129027964 |