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 | 12 |
| 4 | 60 |
| 5 | 440 |
| 6 | 3390 |
| 7 | 33852 |
| 8 | 338072 |
| 9 | 4116240 |
| 10 | 51776730 |
| 11 | 736751180 |
| 12 | 11075784852 |
| 13 | 183142075272 |
| 14 | 3157190863190 |
| 15 | 59336602681020 |
| 16 | 1164223828582320 |
| 17 | 24348331444705952 |
| 18 | 533422896546272562 |
| 19 | 12365952739192923660 |
| 20 | 298208300418298756460 |
| 21 | 7570420981014167756760 |