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 | 4 |
| 1 | 20 |
| 2 | 104 |
| 3 | 552 |
| 4 | 2972 |
| 5 | 16172 |
| 6 | 88720 |
| 7 | 489872 |
| 8 | 2719028 |
| 9 | 15157188 |
| 10 | 84799992 |
| 11 | 475894200 |
| 12 | 2677788492 |
| 13 | 15102309468 |
| 14 | 85347160608 |
| 15 | 483183316512 |
| 16 | 2739851422820 |
| 17 | 15558315261812 |
| 18 | 88462135512712 |
| 19 | 503569008273992 |
| 20 | 2869602773253884 |
| 21 | 16368396446913420 |
| 22 | 93449566652932784 |