A002220 - OEIS

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A002220 as a simple table

n	a(n)
1	1
2	4
3	10
4	30
5	65
6	173
7	343
8	778
9	1518
10	3088
11	5609
12	10959
13	18990
14	34441
15	58903
16	102044
17	167499
18	282519
19	451529
20	737208
21	1160102
22	1836910
23	2828466
24	4410990
25	6670202
26	10161240
27	15186315
28	22758131
29	33480869

[1,4,10,30,65,173,343,778,1518,3088,5609,10959, 18990,34441,58903,102044,167499,282519,451529, 737208,1160102,1836910,2828466,4410990,6670202, 10161240,15186315,22758131,33480869]