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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 10 |
| 4 | 10 |
| 5 | 55 |
| 6 | -1 |
| 7 | 210 |
| 8 | 120 |
| 9 | 120 |
| 10 | 1485 |
| 11 | 2145 |
| 12 | -1 |
| 13 | 2080 |
| 14 | -1 |
| 15 | -1 |
| 16 | 56616 |
| 17 | 1326 |
| 18 | 12561 |
| 19 | -1 |
| 20 | 1540 |
| 21 | 1540 |
| 22 | 21736 |
| 23 | -1 |
| 24 | -1 |
| 25 | 52650 |
| 26 | 16653 |
| 27 | 4950 |
| 28 | 26796 |
| 29 | 10440 |
| 30 | 12880 |
| 31 | 7750 |
| 32 | -1 |
| 33 | -1 |
| 34 | 7140 |
| 35 | 7140 |
| 36 | 154290 |
| 37 | -1 |
| 38 | 11476 |
| 39 | -1 |
| 40 | 214840 |
| 41 | -1 |
| 42 | -1 |
| 43 | 207690 |
| 44 | 23252790 |
| 45 | -1 |
| 46 | -1 |
| 47 | 6895041 |
| 48 | -1 |
| 49 | 750925 |