TOPICS
The cototient of a positive number 
is defined as 
, where 
is the totient function.
It is therefore the number of positive integers 
that have at least one prime factor in common with 
.
The first few cototients for 
,
2, ... are 0, 1, 1, 2, 1, 4, 1, 4, 3, 6, 1, 8, 1, 8, 7, ... (OEIS A051953).
." Colloq. Math. 68,
55-58, 1995.Erdős, P. "Über die Zahlen der Form 
und 
." Elem. Math. 11, 83-86, 1973.Flammenkamp,
A. and Luca, F. "Infinite Families of Noncototients." Colloq. Math. 86,
37-41, 2000.Jamison, R. E. "The Helly Bound for Singular Sums."
Disc. Math. 249, 117-133, 2002.Sloane, N. J. A.
Sequence A051953 in "The On-Line Encyclopedia
of Integer Sequences."Pomerance, C. and Yang, H.-S. "Variant
of a Theorem of Erdős on the Sum-Of-Proper-Divisors Function." Math.
Comput. 83, 1903-1913, 2014.
Weisstein, Eric W. "Cototient." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Cototient.html
