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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | -1 |
| 4 | -1 |
| 5 | -2 |
| 6 | -3 |
| 7 | -6 |
| 8 | -16 |
| 9 | -36 |
| 10 | -91 |
| 11 | -224 |
| 12 | -768 |
| 13 | -2420 |
| 14 | -7854 |
| 15 | -22815 |
| 16 | -73008 |
| 17 | -292864 |
| 18 | -1223040 |
| 19 | -5002998 |
| 20 | -17592960 |
| 21 | -67184000 |
| 22 | -279734796 |
| 23 | -1183614120 |
| 24 | -5844883968 |
| 25 | -29448258840 |
| 26 | -124619677182 |
| 27 | -573333075000 |
| 28 | -2764864302200 |
| 29 | -13664438287500 |