A172020 - cp's OEIS frontend

A172020 Number of subsets S of {1,2,3,...,n} with the property that if x is a member of S then at least one of x-2 and x+2 is also a member of S.

n	a(n)
1	1
2	1
3	2
4	4
5	8
6	16
7	28
8	49
9	84
10	144
11	252
12	441
13	777
14	1369
15	2405
16	4225
17	7410
18	12996
19	22800
20	40000
21	70200
22	123201
23	216216
24	379456
25	665896
26	1168561
27	2050657
28	3598609
29	6315113
30	11082241
31	19448018
32	34128964
33	59892184
34	105103504
35	184443732
36	323676081
37	568011852

[1, 1, 2, 4, 8, 16, 28, 49, 84, 144, 252, 441, 777, 1369, 2405, 4225, 7410, 12996, 22800, 40000, 70200, 123201, 216216, 379456, 665896, 1168561, 2050657, 3598609, 6315113, 11082241, 19448018, 34128964, 59892184, 105103504, 184443732, 323676081, 568011852]

cp's OEIS Frontend

A172020 Number of subsets S of {1,2,3,...,n} with the property that if x is a member of S then at least one of x-2 and x+2 is also a member of S.

Table of values

List of values