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 | 4 |
| 2 | 20 |
| 3 | 132 |
| 4 | 1116 |
| 5 | 12420 |
| 6 | 171300 |
| 7 | 2884980 |
| 8 | 56674380 |
| 9 | 1289511300 |
| 10 | 34769949060 |
| 11 | 1063909626780 |
| 12 | 37255008811020 |
| 13 | 1470406699982220 |
| 14 | 63114539746598340 |
| 15 | 2936218980067393020 |
| 16 | 150241360192861037100 |
| 17 | 8497891914008911514100 |
| 18 | 514514062115556069627060 |