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 | 3 |
| 3 | -1 |
| 4 | 27 |
| 5 | 119 |
| 6 | 1203 |
| 7 | 11759 |
| 8 | 136587 |
| 9 | 1771559 |
| 10 | 25562403 |
| 11 | 405657119 |
| 12 | 7022893947 |
| 13 | 131714582999 |
| 14 | 2660335750803 |
| 15 | 57570797728079 |
| 16 | 1328913670528107 |
| 17 | 32592691757218439 |
| 18 | 846383665814342403 |
| 19 | 23200396829831840639 |
| 20 | 669421949061096575067 |
| 21 | 20281206249626017421879 |