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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 42 |
| 5 | 149 |
| 6 | 568 |
| 7 | 2172 |
| 8 | 8578 |
| 9 | 34181 |
| 10 | 139057 |
| 11 | 569719 |
| 12 | 2364946 |
| 13 | 9881270 |
| 14 | 41674337 |
| 15 | 176735488 |
| 16 | 754733091 |
| 17 | 3238354312 |
| 18 | 13970248201 |
| 19 | 60513360263 |
| 20 | 263262526696 |
| 21 | 1149346431161 |
| 22 | 5035888179481 |
| 23 | 22132171128821 |
| 24 | 97564507265020 |
| 25 | 431236737233659 |
| 26 | 1911053967488337 |
| 27 | 8488822597541547 |
[1,1,4,12,42,149,568,2172,8578,34181,139057, 569719,2364946,9881270,41674337,176735488, 754733091,3238354312,13970248201,60513360263, 263262526696,1149346431161,5035888179481, 22132171128821,97564507265020,431236737233659, 1911053967488337,8488822597541547] |