A221792 - OEIS

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A221792 as a simple table

n	a(n)
1	1
2	3
3	7
4	17
5	36
6	109
7	265
8	762
9	2125
10	5964
11	17205
12	49989
13	145047
14	424155
15	1250298
16	3697457
17	10985390
18	32768938
19	98054446
20	294239322
21	885300000
22	2669959359
23	8069333311
24	24435519147

[1,3,7,17,36,109,265,762,2125,5964,17205,49989, 145047,424155,1250298,3697457,10985390,32768938, 98054446,294239322,885300000,2669959359, 8069333311,24435519147]