A357898 - cp's OEIS frontend

A357898 a(n) is the least k such that phi(k) + d(k) = 2^n, or -1 if there is no such k, where phi(k) = A000010(k) is Euler's totient function and d(k) = A000005(k) is the number of divisors of k.

n	a(n)
1	1
2	3
3	7
4	21
5	31
6	77
7	127
8	301
9	783
10	1133
11	3399
12	4781
13	8191
14	16637
15	37367
16	101601
17	131071
18	305837
19	524287
20	1073581
21	3220743
22	4201133
23	8544103
24	18404669
25	34012327
26	67139117
27	135255431
28	300528877
29	824583699
30	1073862029
31	2147483647
32	4295564381
33	8603449703
34	25807607829

[1, 3, 7, 21, 31, 77, 127, 301, 783, 1133, 3399, 4781, 8191, 16637, 37367, 101601, 131071, 305837, 524287, 1073581, 3220743, 4201133, 8544103, 18404669, 34012327, 67139117, 135255431, 300528877, 824583699, 1073862029, 2147483647, 4295564381, 8603449703, 25807607829]

cp's OEIS Frontend

A357898 a(n) is the least k such that phi(k) + d(k) = 2^n, or -1 if there is no such k, where phi(k) = A000010(k) is Euler's totient function and d(k) = A000005(k) is the number of divisors of k.

Table of values

List of values