| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 60 |
| 4 | 216 |
| 5 | 768 |
| 6 | 2728 |
| 7 | 9704 |
| 8 | 34552 |
| 9 | 123064 |
| 10 | 438328 |
| 11 | 1561176 |
| 12 | 5560248 |
| 13 | 19803096 |
| 14 | 70529656 |
| 15 | 251194904 |
| 16 | 894643768 |
| 17 | 3186321112 |
| 18 | 11348251384 |
| 19 | 40417397400 |
| 20 | 143948695992 |
| 21 | 512680882776 |
| 22 | 1825940038264 |
| 23 | 6503181876248 |
| 24 | 23161425701176 |
| 25 | 82490640856024 |
| 26 | 293794773978616 |
| 27 | 1046365603664280 |
[1,4,16,60,216,768,2728,9704,34552,123064,438328, 1561176,5560248,19803096,70529656,251194904, 894643768,3186321112,11348251384,40417397400, 143948695992,512680882776,1825940038264, 6503181876248,23161425701176,82490640856024, 293794773978616,1046365603664280] |