%N Number of distinct prime signatures represented among the unitary divisors of A025487(n).
%C a(n) = number of members m of A025487 such that d(m^k) divides d(A025487(n)^k) for all values of k. (Here d(n) represents the number of divisors of n, or A000005(n).)
%H Amiram Eldar, <a href="/A182861/b182861.txt">Table of n, a(n) for n = 1..10000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/UnitaryDivisor.html">Unitary Divisor</a>
%F a(n) = A000005(A181820(n)).
%F If the canonical factorization of n into prime powers is Product p^e(p), then the formula for d(n^k) is Product_p (ek + 1). (See also A146289, A146290.)
%e 60 has 8 unitary divisors (1, 3, 4, 5, 12, 15, 20 and 60). Primes 3 and 5 have the same prime signature, as do 12 (2^2*3) and 20 (2^2*5); each of the other four numbers listed is the only unitary divisor of 60 with its particular prime signature. Since a total of 6 distinct prime signatures appear among the unitary divisors of 60, and since 60 = A025487(13), a(13) = 6.
%Y Cf. A000005, A025487, A034444, A085082, A146289, A146290, A181820, A182860, A182862.
%A _Matthew Vandermast_, Jan 14 2011
%E More terms from _Amiram Eldar_, Jun 20 2019