OFFSET
1,1
COMMENTS
Composite numbers m have nondivisors k in the cototient such that k | n^e with e > 1. These k appear in row n of A272618 and are enumerated by A243822(n). These nondivisors k are a kind of "regular" number along with divisors d of n; both are listed in row n of A162306 and are together enumerated by A045763(n). Divisors of n are listed in row n of A027750.
This sequence lists numbers that have an equal number of nondivisors k in the cototient of n as divisors d.
The smallest odd term is 105.
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
EXAMPLE
MATHEMATICA
Select[Range@ 600, Function[n, Count[Range[n], _?(PowerMod[n, Floor@ Log2@ n, #] == 0 &)] == 2 DivisorSigma[0, n]]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael De Vlieger, Feb 26 2018
STATUS
approved