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 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 104 |
| 5 | 529 |
| 6 | 2700 |
| 7 | 13845 |
| 8 | 71120 |
| 9 | 365697 |
| 10 | 1881236 |
| 11 | 9679605 |
| 12 | 49809720 |
| 13 | 256324433 |
| 14 | 1319090972 |
| 15 | 6788338869 |
| 16 | 34934465440 |
| 17 | 179781713537 |
| 18 | 925203573540 |
| 19 | 4761340669269 |
| 20 | 24503114321416 |
| 21 | 126099496024593 |
| 22 | 648941324534188 |
| 23 | 3339623572751061 |
| 24 | 17186585699725680 |