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 | 0 |
| 3 | 3 |
| 4 | 6 |
| 5 | 0 |
| 6 | 12 |
| 7 | 106 |
| 8 | 420 |
| 9 | 2718 |
| 10 | 18240 |
| 11 | 120879 |
| 12 | 694320 |
| 13 | 5430438 |
| 14 | 40668264 |
| 15 | 300401818 |
| 16 | 2369504386 |
| 17 | 19928714475 |
| 18 | 174151735920 |
| 19 | 1543284732218 |
| 20 | 14224347438876 |
| 21 | 135649243229688 |
| 22 | 1331658133954940 |
| 23 | 13369350846412794 |
| 24 | 138122850643702056 |
| 25 | 1462610254141337590 |