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| n | a(n) |
|---|---|
| 1 | 21 |
| 2 | 237 |
| 3 | 311 |
| 4 | 1660 |
| 5 | 8761 |
| 6 | 31433 |
| 7 | 130402 |
| 8 | 585212 |
| 9 | 2366785 |
| 10 | 9815061 |
| 11 | 42205654 |
| 12 | 175355823 |
| 13 | 730455300 |
| 14 | 3093042582 |
| 15 | 12946456110 |
| 16 | 54109637656 |
| 17 | 227779656571 |
| 18 | 955289842419 |
| 19 | 4000305391990 |
| 20 | 16801782691536 |
| 21 | 70493554918254 |
[21,237,311,1660,8761,31433,130402,585212,2366785, 9815061,42205654,175355823,730455300,3093042582, 12946456110,54109637656,227779656571,955289842419, 4000305391990,16801782691536,70493554918254] |