OFFSET
1,6
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..24914
EXAMPLE
For n = 22, with proper divisors [1, 2, 11], only 2 is in A001608, thus a(22) = 1.
For n = 121, with proper divisors [1, 11], neither of them is in A001608, thus a(121) = 0. Note that this is the first zero not in A008578.
For n = 644, with proper divisors [1, 2, 4, 7, 14, 23, 28, 46, 92, 161, 322, 644], both 2 and 7 are in A001608, thus a(644) = 2.
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 10 2017
STATUS
approved