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 | 10 |
| 2 | -45 |
| 3 | 450 |
| 4 | -5535 |
| 5 | 75600 |
| 6 | -1106100 |
| 7 | 16953750 |
| 8 | -268652880 |
| 9 | 4365638550 |
| 10 | -72354858300 |
| 11 | 1218356280000 |
| 12 | -20784495119850 |
| 13 | 358457180010750 |
| 14 | -6239532583193625 |
| 15 | 109476057598087500 |
| 16 | -1934128026918961515 |
| 17 | 34378012275668994150 |
| 18 | -614328464414815220025 |
| 19 | 11030366153872043358750 |
| 20 | -198899407327466712808800 |
| 21 | 3600377821710426377668500 |