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 | 0 |
| 2 | -1 |
| 3 | -3 |
| 4 | -9 |
| 5 | -35 |
| 6 | -195 |
| 7 | -1477 |
| 8 | -13839 |
| 9 | -151335 |
| 10 | -1877745 |
| 11 | -26022491 |
| 12 | -398318481 |
| 13 | -6674043961 |
| 14 | -121496905803 |
| 15 | -2387748622365 |
| 16 | -50382638237343 |
| 17 | -1136006690370371 |
| 18 | -27257495551671753 |
| 19 | -693436310776781083 |
| 20 | -18643640290958926785 |
| 21 | -528196548501606911913 |