OFFSET
1,1
COMMENTS
Numbers whose first, second or third arithmetic is prime (A157037, A192192, A328239) are all included in this sequence, because: (1) taking arithmetic derivative of a prime gives 1, which is squarefree, (2) primes themselves are squarefree, and (3) only squarefree numbers may have arithmetic derivative that is a prime.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=6, its first arithmetic derivative is A003415(6) = 5, and its second derivative is A003415(5) = 1, and 1 is a squarefree number (in A005117), thus 6 is included in this sequence.
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Oct 11 2019
STATUS
approved