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 | 2 |
| 3 | -1 |
| 4 | 6 |
| 5 | -6 |
| 6 | -1 |
| 7 | 12 |
| 8 | -30 |
| 9 | 20 |
| 10 | -1 |
| 11 | 20 |
| 12 | -90 |
| 13 | 140 |
| 14 | -70 |
| 15 | -1 |
| 16 | 30 |
| 17 | -210 |
| 18 | 560 |
| 19 | -630 |
| 20 | 252 |
| 21 | -1 |
| 22 | 42 |
| 23 | -420 |
| 24 | 1680 |
| 25 | -3150 |
| 26 | 2772 |
| 27 | -924 |
| 28 | -1 |
| 29 | 56 |
| 30 | -756 |
| 31 | 4200 |
| 32 | -11550 |
| 33 | 16632 |
| 34 | -12012 |
| 35 | 3432 |
| 36 | -1 |
| 37 | 72 |
| 38 | -1260 |
| 39 | 9240 |
| 40 | -34650 |
| 41 | 72072 |
| 42 | -84084 |
| 43 | 51480 |
| 44 | -12870 |
| 45 | -1 |
| 46 | 90 |
| 47 | -1980 |
| 48 | 18480 |
| 49 | -90090 |
| 50 | 252252 |
| 51 | -420420 |
| 52 | 411840 |
| 53 | -218790 |
| 54 | 48620 |
| 55 | -1 |
| 56 | 110 |
| 57 | -2970 |
| 58 | 34320 |
| 59 | -210210 |
| 60 | 756756 |
| 61 | -1681680 |
| 62 | 2333760 |
| 63 | -1969110 |
| 64 | 923780 |
| 65 | -184756 |