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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 22 |
| 3 | 146 |
| 4 | 1013 |
| 5 | 7269 |
| 6 | 53156 |
| 7 | 394154 |
| 8 | 2951950 |
| 9 | 22279439 |
| 10 | 169175927 |
| 11 | 1290970376 |
| 12 | 9891573310 |
| 13 | 76050920691 |
| 14 | 586426828071 |
| 15 | 4533349152056 |
| 16 | 35122039919110 |
| 17 | 272634162463779 |
| 18 | 2119948044144136 |
| 19 | 16509519223752380 |
| 20 | 128747868290672353 |
| 21 | 1005273235488567875 |
[1,4,22,146,1013,7269,53156,394154,2951950, 22279439,169175927,1290970376,9891573310, 76050920691,586426828071,4533349152056, 35122039919110,272634162463779,2119948044144136, 16509519223752380,128747868290672353, 1005273235488567875] |