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 | 30 |
| 3 | 260 |
| 4 | 2465 |
| 5 | 24796 |
| 6 | 260008 |
| 7 | 2811216 |
| 8 | 31117240 |
| 9 | 350890260 |
| 10 | 4016744586 |
| 11 | 46556054072 |
| 12 | 545273713228 |
| 13 | 6443442857024 |
| 14 | 76727957438650 |
| 15 | 919796418086076 |
| 16 | 11091249210406816 |
| 17 | 134439965189940176 |
| 18 | 1637160457090585016 |
| 19 | 20019920157735604796 |
| 20 | 245733987135102838131 |