A216957 - cp's OEIS frontend

A216957 a(1)=2; for n > 1, a(n) = 2^(n-2) + (1/(2n-2)) * Sum_{ d divides n-1 } phi(2d)*2^((n-1)/d).

n	a(n)
1	2
2	2
3	4
4	6
5	12
6	20
7	40
8	74
9	148
10	286
11	568
12	1118
13	2228
14	4412
15	8788
16	17480
17	34836
18	69392
19	138388
20	275942
21	550560
22	1098516
23	2192572
24	4376666
25	8738324
26	17448308
27	34845304
28	69594398
29	139011816
30	277691852
31	554767744
32	1108378658
33	2214594580
34	4425117884
35	8842583584
36	17670722600
37	35314182976
38	70576759892
39	141055781836

[2, 2, 4, 6, 12, 20, 40, 74, 148, 286, 568, 1118, 2228, 4412, 8788, 17480, 34836, 69392, 138388, 275942, 550560, 1098516, 2192572, 4376666, 8738324, 17448308, 34845304, 69594398, 139011816, 277691852, 554767744, 1108378658, 2214594580, 4425117884, 8842583584, 17670722600, 35314182976, 70576759892, 141055781836]

cp's OEIS Frontend

A216957 a(1)=2; for n > 1, a(n) = 2^(n-2) + (1/(2n-2)) * Sum_{ d divides n-1 } phi(2d)*2^((n-1)/d).

Table of values

List of values