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 | 1 |
| 4 | 1 |
| 5 | -119 |
| 6 | -719 |
| 7 | -2519 |
| 8 | -6719 |
| 9 | -15119 |
| 10 | 1784161 |
| 11 | 19902961 |
| 12 | 119655361 |
| 13 | 518763961 |
| 14 | 1815974161 |
| 15 | -212497445159 |
| 16 | -3472602456959 |
| 17 | -29605333299359 |
| 18 | -177764320560959 |
| 19 | -844590032480159 |
| 20 | 97992221659873921 |
| 21 | 2116963290135836521 |
| 22 | 23379513665735470321 |