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 | 5 |
| 3 | 30 |
| 4 | 255 |
| 5 | 2275 |
| 6 | 21476 |
| 7 | 210404 |
| 8 | 2120041 |
| 9 | 21830314 |
| 10 | 228713056 |
| 11 | 2430255074 |
| 12 | 26128088701 |
| 13 | 283703487059 |
| 14 | 3106713300821 |
| 15 | 34270543858459 |
| 16 | 380471319687826 |
| 17 | 4247891403168599 |
| 18 | 47665096853113576 |
| 19 | 537244509843680309 |
| 20 | 6079834137116933061 |
| 21 | 69054467456964456599 |