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) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 45 |
| 6 | 189 |
| 7 | 588 |
| 8 | 2352 |
| 9 | 7560 |
| 10 | 29700 |
| 11 | 98010 |
| 12 | 382239 |
| 13 | 1288287 |
| 14 | 5010005 |
| 15 | 17177160 |
| 16 | 66745536 |
| 17 | 232092432 |
| 18 | 901995588 |
| 19 | 3173688180 |
| 20 | 12342120700 |
| 21 | 43861998180 |
| 22 | 170724392916 |
| 23 | 611947174608 |
| 24 | 2384209771200 |
| 25 | 8609646396000 |
| 26 | 33577620944400 |
| 27 | 122041737663300 |
| 28 | 476432168185575 |