A067980 - OEIS

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A067980 as a simple table

n	a(n)
0	3
1	13
2	31
3	69
4	140
5	274
6	519
7	963
8	1757
9	3165
10	5642
11	9972
12	17499
13	30521
14	52955
15	91461
16	157336
17	269702
18	460863
19	785295
20	1334713
21	2263293
22	3829846
23	6468264
24	10905075
25	18355429
26	30849559
27	51776133
28	86785892

[3,13,31,69,140,274,519,963,1757,3165,5642,9972, 17499,30521,52955,91461,157336,269702,460863, 785295,1334713,2263293,3829846,6468264,10905075, 18355429,30849559,51776133,86785892]