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 | 0 |
| 2 | 6 |
| 3 | 9 |
| 4 | 120 |
| 5 | 555 |
| 6 | 5148 |
| 7 | 39711 |
| 8 | 378528 |
| 9 | 3715011 |
| 10 | 39838260 |
| 11 | 452684463 |
| 12 | 5463506304 |
| 13 | 69553644771 |
| 14 | 930940368036 |
| 15 | 13054086036855 |
| 16 | 191222363275968 |
| 17 | 2918620069099395 |
| 18 | 46309955947643124 |
| 19 | 762335523354333855 |
| 20 | 12995722456718984160 |
| 21 | 229045407317491457763 |