OFFSET
1,3
LINKS
Rémy Sigrist, Table of n, a(n) for n = 1..10000
FORMULA
a(A002110(n)) = 1.
EXAMPLE
a(11)=8 since 2,3,4,5,7,8,9,11 each have one distinct prime factor. a(12)=3 since 6,10,12 each have two distinct prime factors.
From Gus Wiseman, Dec 28 2018: (Start)
Column n lists the a(n) positive integers less than or equal to n with the same number of distinct prime factors as n:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
---------------------------------------------------------------------
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
2 3 4 5 7 8 6 9 10 11 12 14 13 16 15 17 18
2 3 4 5 7 8 6 9 10 12 11 13 14 16 15
2 3 4 5 7 8 6 10 9 11 12 13 14
2 3 4 5 7 6 8 9 10 11 12
2 3 4 5 7 8 6 9 10
2 3 4 5 7 8 6
2 3 4 5 7
2 3 4 5
2 3 4
2 3
2
(End)
MATHEMATICA
Table[Length[Select[Range[n], PrimeNu[#]==PrimeNu[n]&]], {n, 100}] (* Gus Wiseman, Dec 28 2018 *)
PROG
(PARI) a(n) = my(nb = #factor(n)~); sum(k=1, n, #factor(k)~ == nb); \\ Michel Marcus, Jul 13 2019
CROSSREFS
Positions of 1's are A002110.
KEYWORD
nonn,look
AUTHOR
Henry Bottomley, Dec 21 2001
STATUS
approved