A278613 - OEIS

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A278613 as a simple table

n	a(n)
0	3
1	8
2	21
3	55
4	145
5	381
6	1001
7	2633
8	6921
9	18193
10	47833
11	125745
12	330569
13	869057
14	2284665
15	6006193
16	15789865
17	41510241
18	109127129
19	286886801

[3,8,21,55,145,381,1001,2633,6921,18193,47833, 125745,330569,869057,2284665,6006193,15789865, 41510241,109127129,286886801]