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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 206 |
| 4 | 1815 |
| 5 | 17082 |
| 6 | 168159 |
| 7 | 1710234 |
| 8 | 17828973 |
| 9 | 189504744 |
| 10 | 2045971440 |
| 11 | 22374997320 |
| 12 | 247344411792 |
| 13 | 2759394009008 |
| 14 | 31027178033064 |
| 15 | 351270123392892 |
| 16 | 4000793799046578 |
| 17 | 45809545263096832 |
| 18 | 527010005799822844 |
| 19 | 6088666065809281348 |
| 20 | 70612995488695876634 |
[1,4,26,206,1815,17082,168159,1710234,17828973, 189504744,2045971440,22374997320,247344411792, 2759394009008,31027178033064,351270123392892, 4000793799046578,45809545263096832, 527010005799822844,6088666065809281348, 70612995488695876634] |