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 | -21 |
| 7 | 53 |
| 8 | -137 |
| 9 | 362 |
| 10 | -971 |
| 11 | 2642 |
| 12 | -7272 |
| 13 | 20211 |
| 14 | -56631 |
| 15 | 159795 |
| 16 | -453650 |
| 17 | 1294797 |
| 18 | -3713100 |
| 19 | 10693036 |
| 20 | -30910440 |
| 21 | 89657680 |
| 22 | -260860962 |
| 23 | 761114168 |
| 24 | -2226409022 |
| 25 | 6528039545 |
| 26 | -19182376302 |
| 27 | 56479676608 |
| 28 | -166605140314 |
| 29 | 492304708589 |
| 30 | -1457061274821 |
| 31 | 4318906269671 |