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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 112 |
| 5 | 615 |
| 6 | 3432 |
| 7 | 19382 |
| 8 | 110432 |
| 9 | 633555 |
| 10 | 3654840 |
| 11 | 21179389 |
| 12 | 123195360 |
| 13 | 718887585 |
| 14 | 4206458700 |
| 15 | 24671967210 |
| 16 | 145008786304 |
| 17 | 853852037038 |
| 18 | 5035940194824 |
| 19 | 29744992814381 |
| 20 | 175921665090480 |
| 21 | 1041700117634505 |
| 22 | 6175002739467276 |
[1,4,21,112,615,3432,19382,110432,633555,3654840, 21179389,123195360,718887585,4206458700, 24671967210,145008786304,853852037038, 5035940194824,29744992814381,175921665090480, 1041700117634505,6175002739467276] |