OFFSET
1,2
COMMENTS
The index of a prime number n is the number m such that n is the m-th prime.
The asymptotic density of this sequence is (1/2) * Product_{p in A006450} (1 - 1/p) = 1/(2*Sum_{n>=1} 1/A076610(n)) < 1/6. - Amiram Eldar, Feb 02 2021
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
The sequence of terms begins:
1 = 1
7 = prime(4)
13 = prime(6)
19 = prime(8)
23 = prime(9)
29 = prime(10)
37 = prime(12)
43 = prime(14)
47 = prime(15)
49 = prime(4)^2
53 = prime(16)
61 = prime(18)
71 = prime(20)
73 = prime(21)
79 = prime(22)
89 = prime(24)
91 = prime(4)*prime(6)
97 = prime(25)
101 = prime(26)
103 = prime(27)
107 = prime(28)
113 = prime(30)
131 = prime(32)
133 = prime(4)*prime(8)
137 = prime(33)
139 = prime(34)
149 = prime(35)
151 = prime(36)
161 = prime(4)*prime(9)
MATHEMATICA
Select[Range[1, 100, 2], And@@Not/@PrimeQ/@PrimePi/@First/@FactorInteger[#]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 18 2018
STATUS
approved