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 | 3 |
| 3 | 12 |
| 4 | 45 |
| 5 | 180 |
| 6 | 721 |
| 7 | 2940 |
| 8 | 12069 |
| 9 | 49935 |
| 10 | 207691 |
| 11 | 867900 |
| 12 | 3640429 |
| 13 | 15319395 |
| 14 | 64643580 |
| 15 | 273431408 |
| 16 | 1158988141 |
| 17 | 4921651521 |
| 18 | 20934115963 |
| 19 | 89173404140 |
| 20 | 380355072153 |
| 21 | 1624282578215 |
| 22 | 6943928981859 |
| 23 | 29715239620368 |
| 24 | 127276313406125 |
| 25 | 545605497876400 |
| 26 | 2340694589348376 |
| 27 | 10048952593607088 |
| 28 | 43170264470594302 |