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 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | 1 |
| 5 | -10 |
| 6 | 9 |
| 7 | -1 |
| 8 | 91 |
| 9 | -315 |
| 10 | 225 |
| 11 | 1 |
| 12 | -820 |
| 13 | 8694 |
| 14 | -18900 |
| 15 | 11025 |
| 16 | -1 |
| 17 | 7381 |
| 18 | -224730 |
| 19 | 1143450 |
| 20 | -1819125 |
| 21 | 893025 |
| 22 | 1 |
| 23 | -66430 |
| 24 | 5684679 |
| 25 | -61647300 |
| 26 | 203378175 |
| 27 | -255405150 |
| 28 | 108056025 |
| 29 | -1 |
| 30 | 597871 |
| 31 | -142714845 |
| 32 | 3162834675 |
| 33 | -19494349875 |
| 34 | 47377655325 |
| 35 | -49165491375 |
| 36 | 18261468225 |
| 37 | 1 |
| 38 | -5380840 |
| 39 | 3573251964 |
| 40 | -158546770200 |
| 41 | 1734021238950 |
| 42 | -7311738634200 |
| 43 | 14041664336700 |
| 44 | -12417798393000 |
| 45 | 4108830350625 |
| 46 | -1 |
| 47 | 48427561 |
| 48 | -89379726660 |
| 49 | 7858123038900 |
| 50 | -148224512094750 |
| 51 | 1025176095093150 |
| 52 | -3257761647640500 |
| 53 | 5167045911327300 |
| 54 | -3981456609755625 |
| 55 | 1187451971330625 |