OFFSET
1,2
COMMENTS
A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = Product_{p in A006450} (1 + 1/(p*(p-1))) = 1.24410463... - Amiram Eldar, May 04 2022
EXAMPLE
The terms together with their prime indices (not prime factors) begin:
1: {}
9: {2,2}
25: {3,3}
27: {2,2,2}
81: {2,2,2,2}
121: {5,5}
125: {3,3,3}
225: {2,2,3,3}
243: {2,2,2,2,2}
289: {7,7}
625: {3,3,3,3}
675: {2,2,2,3,3}
729: {2,2,2,2,2,2}
961: {11,11}
For example, 675 = prime(2)^3 prime(3)^2 = 3^3 * 5^2.
MATHEMATICA
Select[Range[1000], #==1||And@@PrimeQ/@PrimePi/@First/@FactorInteger[#]&&Min@@Last/@FactorInteger[#]>1&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 24 2022
STATUS
approved