0068. Cracking' RSA

Имя входного файла:	rsa.in
Имя выходного файла:	rsa.out
Ограничение по времени:	1 s
Ограничение по памяти:	64 megabytes

The following problem is somehow related to the final stage of many famous integer factorization algorithms involved in some cryptoanalytical problems, for example cracking well-known RSA public key system.

The most powerful of such algorithms, so called quadratic sieve descendant algorithms utilize the fact that if n = pq where p and q are large unknown primes needed to be found out, then if v²=w² mod n and u ≠ ± v mod n then gcd(v + w, n) is a factor of n (either p or q).

Not getting further in the details of these algorithms, let us consider our problem. Given m integer numbers b₁, b₂, …, b_m such that all their prime factors are from the set of first t primes, the task is to find such S ⊂ {1, 2, …, m} that ∏_i∈Sb_i is a perfect square i.e.  equal to u² for some integer u. Given such S we get one pair for testing (product of S elements stands for v when w is known from other steps of algorithms which are of no interest to us, testing performed is checking whether pair is nontrivial, i.e. u ≠ ± v mod n). Since we want to factor n with maximum possible probability, we would like to get as many such sets as possible. So the interesting problem could be to calculate the number of all such sets. This is exactly your task.

Input file

The first line of the input file contains two integers t and m (1 ≤ t ≤ 100, 1 ≤ m ≤ 100). The second line of the input file contains m integer numbers b_i such that all their prime factors are from t first primes (for example, if t = 3 all their prime factors are from the set {2, 3, 5}). 1 ≤ b_i ≤ 10⁹ for all i.

Output file

Output the number of non-empty subsets of the given set {b_i}, the product of numbers from which is a perfect square

Examples:

rsa.in	rsa.out
3 4 9 20 500 3	3

Источник: Petrozavodsk Winter 2003. St. Petersburg Contest I

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