OFFSET
1,2
COMMENTS
a(n) is the smallest positive integer k such that A033716(k) = 2*n,
FORMULA
If p is prime, a(p) = 7^(p-1).
a(n) is divisible by 7 for n > 3.
EXAMPLE
n | a(n)
------------+-------------------------------------
2 | 7.
3 = 3*1 | 4.
4 | 91 = 7 * 13.
5 | 2401 = 7^4.
6 = 3*2 | 28 = 4 * 7.
7 | 117649 = 7^6.
8 | 1729 = 7 * 13 * 19.
9 = 3*3 | 196 = 4 * 7^2.
10 | 31213 = 7^4 * 13.
11 | 282475249 = 7^10.
12 = 3*4 | 364 = 4 * 7 * 13.
13 | 13841287201 = 7^12.
14 | 1529437 = 7^6 * 13.
15 = 3*5 | 9604 = 4 * 7^4.
16 | 53599 = 7 * 13 * 19 * 31.
17 | 7^16.
18 = 3*6 | 2548 = 4 * 7^2 * 13.
19 | 7^18.
20 | 593047 = 7^4 * 13 * 19.
21 = 3*7 | 470596 = 4 * 7^6.
22 | 3672178237 = 7^10 * 13.
23 | 7^22.
24 = 3*8 | 6916 = 4 * 7 * 13 * 19.
25 | 68574961 = 7^4 * 13^4.
26 | 179936733613 = 7^12 * 13.
27 = 3*9 | 33124 = 4 * 7^2 * 13^2.
28 | 29059303 = 7^6 * 13 * 19.
29 | 7^28.
30 = 3*10 | 124852 = 4 * 7^4 * 13.
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 02 2024
STATUS
approved