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 | -5 |
| 3 | 19 |
| 4 | 1 |
| 5 | -1103 |
| 6 | 15211 |
| 7 | -123821 |
| 8 | 120865 |
| 9 | 19464193 |
| 10 | -474727877 |
| 11 | 7017193075 |
| 12 | -50549088671 |
| 13 | -931708750607 |
| 14 | 49742453940331 |
| 15 | -1276858353426317 |
| 16 | 21239149342811329 |
| 17 | -100057086073774463 |
| 18 | -9091588769200298501 |
| 19 | 454849803186974314579 |
| 20 | -13529950476868715792063 |
| 21 | 262961916344710204693681 |