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a(n) first deviates from b(n) = 2*A079275(n) at a(210) = 14 <> b(210) = 12. - Georg Fischer, May 23 2024
a(n) = 2^omega(n) - 2 (for n > 1) = 2*A079275(n).
Number of numbers m satisfying 1 < m < n such that m^2= == m (mod n).
Cf. A001221, A007875, A034444, A079275, A309307.
The number of nontrivial unitary divisors of n (i.e., excluding 1 and n). - Amiram Eldar, May 29 2020
a(n) = 2^{^omega(n)} - ) - 2 = (for n > 1) = 2*A079275(n).
