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.
All squarefree terms are even.
EXAMPLE
The prime indices of 1617 are {2,4,4,5}, with distinct divisors {1,2,4,5}, so 1617 is in the sequence.
The terms together with their prime indices begin:
1: {}
2: {1}
6: {1,2}
9: {2,2}
10: {1,3}
22: {1,5}
25: {3,3}
28: {1,1,4}
30: {1,2,3}
34: {1,7}
42: {1,2,4}
45: {2,2,3}
62: {1,11}
63: {2,2,4}
66: {1,2,5}
75: {2,3,3}
82: {1,13}
92: {1,1,9}
98: {1,4,4}
99: {2,2,5}
102: {1,2,7}
104: {1,1,1,6}
MATHEMATICA
Select[Range[100], PrimeOmega[#]==Length[Union @@ Divisors/@PrimePi/@First/@If[#==1, {}, FactorInteger[#]]]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 14 2024
STATUS
approved