import java.util.Scanner

import scala.collection.immutable.Stack
import scala.collection.mutable.ArrayBuffer

object Main {
  private val Mod = (1e9 + 7).toInt
  private val Fact = {
    var cur = 1L
    for (i <- 0 to 200000) yield {
      if (i == 0) {
        1
      } else {
        cur = (cur * i) % Mod
        cur
      }
    }
  }
  private val Pow = {
    val pow = new Array[Int](200000)
    pow(0) = 1
    for (i <- 1 until pow.length) pow(i) = pow(i - 1) * 2 % Mod
    pow
  }

  def main(args: Array[String]): Unit = {
    val in = new Scanner(System.in)
    while (true) {
      val n = in.nextInt()
      if (n == 0) {
        return
      }
      val a = for (_ <- 0 until n) yield {
        in.nextInt() - 1
      }
      println(solve(a.toArray))
    }
  }

  def cycleCheck(graph: IndexedSeq[Seq[Int]]): Boolean = {
    val cmp = StronglyConnectedComponents.decompose(graph)
    var map = Map[Int, Int]()
    cmp.foreach { c => map += (c -> (map.getOrElse(c, 0) + 1)) }
    map.values.forall(count => count <= 2)
  }

  def pathCheck(graph: IndexedSeq[Seq[Int]]): Boolean = {
    val uf = new UnionFind(graph.size)
    for {
      i <- graph.indices
      j <- graph(i)
    } uf.unite(i, j)

    var map = Map[Int, Int]()
    for {
      i <- graph.indices
      if graph(i).isEmpty
    } {
      val count = map.getOrElse(uf.find(i), 0)
      map += (uf.find(i) -> (count + 1))
    }
    map.values.forall(count => count <= 2)
  }

  def getSize(array: Array[Int]): (Int, Int) = {
    val N = array.length
    val uf = new UnionFind(N)
    for (i <- array.indices) uf.unite(i, array(i))
    val sizes = for {
      i <- 0 until N
      if i == 0 || !uf.isSame(i, 0)
    } yield {
      if (i == 0) {
        uf.partialSizeOf(i)
      } else {
        val s = uf.partialSizeOf(i)
        uf.unite(i, 0)
        s
      }
    }

    var three = 0
    var two = 0
    sizes.foreach(size => if (size == 2) {
      two += 1
    } else {
      three += 1
    })

    (two, three)
  }

  def solve(parent: Array[Int]): Int = {
    val n = parent.length
    val combination = new Combination(n + 1, Mod)

    val graph = parent.indices.map(i => new ArrayBuffer[Int]())
    parent.indices.foreach(i => graph(parent(i)).append(i))

    if (cycleCheck(graph) && pathCheck(graph)) {
      val (two, three) = getSize(parent)
      if (three == 0) {
        var cur: Long = ((two + 2) / 2) % Mod
        cur = cur * Pow(two) % Mod
        cur = cur * Fact(two) % Mod
        cur.toInt
      } else {
        var ans = 0L
        for (i <- 0 to math.min(two + three - 2, two)) {
          var cur = combination.get(two + three - i - 2, two - i).toLong
          cur = cur * Fact(two) % Mod
          cur = cur * Fact(three) % Mod
          cur = cur * Pow(two + three) % Mod
          cur = cur * (two + three - i - 1) % Mod
          cur = cur * ((i + 2) / 2) % Mod
          ans = (ans + cur) % Mod
        }
        for (i <- 0 to math.min(two + three - 1, two)) {
          var cur = combination.get(two + three - i - 1, two - i).toLong
          cur = cur * Fact(two) % Mod
          cur = cur * Fact(three) % Mod
          cur = cur * Pow(two + three) % Mod
          cur = cur * ((i + 2) / 2) % Mod
          ans = (ans + cur * 2) % Mod
        }
        ans.toInt
      }
    } else {
      0
    }
  }

  class UnionFind(n: Int) {
    private val parent = (0 until n).toArray
    private val sizes = Array.fill[Int](n)(1)
    private var _size = n

    def find(x: Int): Int = {
      if (x == parent(x)) {
        x
      } else {
        parent(x) = find(parent(x))
        parent(x)
      }
    }

    def unite(a: Int, b: Int): Boolean = {
      val fa = find(a)
      val fb = find(b)
      if (fa == fb) {
        false
      } else {
        val (x, y) = if (sizes(fa) >= sizes(fb)) {
          (fa, fb)
        } else {
          (fb, fa)
        }

        parent(y) = x
        sizes(x) += sizes(y)
        sizes(y) = 0

        _size -= 1
        true
      }
    }

    def isSame(x: Int, y: Int): Boolean = find(x) == find(y)

    def partialSizeOf(x: Int): Int = sizes(find(x))

    def size(): Int = _size
  }

  class Combination(max: Int, mod: Int) {
    private val inv = new Array[Long](max + 1)
    private val fact = new Array[Long](max + 1)
    private val invFact = new Array[Long](max + 1)
    inv(1) = 1
    for (i <- 2 to max) inv(i) = inv(mod % i) * (mod - mod / i) % mod
    fact(0) = 1
    invFact(0) = 1
    for (i <- 1 to max) fact(i) = (fact(i - 1) * i) % mod
    for (i <- 1 to max) invFact(i) = (invFact(i - 1) * inv(i)) % mod

    /**
      * get nCm
      */
    def get(n: Int, m: Int): Int = {
      if (n < m) {
        0
      } else fact(n) * invFact(m) % mod * invFact(n - m) % mod
    }.toInt
  }

  object StronglyConnectedComponents {
    def decompose(graph: IndexedSeq[Seq[Int]]): Array[Int] = {
      val vs = new ArrayBuffer[Int]()
      val V = graph.size
      val cmp = new Array[Int](V)

      val rg = graph.indices.map(_ => new ArrayBuffer[Int]())
      for {
        from <- graph.indices
        to <- graph(from)
      } rg(to).append(from)

      var used = Array.fill[Boolean](V)(false)
      var stack = new Stack[Int]()
      val added = Array.fill[Boolean](V)(false)
      for {
        i <- used.indices
        if !used(i)
      } {
        stack = stack.push(i)
        while (stack.nonEmpty) {
          val v = stack.top
          used(v) = true
          var pushed = false
          for {
            u <- graph(v).reverse
            if !used(u)
          } {
            stack = stack.push(u)
            pushed = true
          }
          if (!pushed) {
            stack = stack.pop
            if (!added(v)) {
              vs.append(v)
              added(v) = true
            }
          }
        }
      }

      used = Array.fill[Boolean](V)(false)
      var k = 0
      for {
        i <- vs.reverse
        if !used(i)
      } {
        stack = stack.push(i)
        used(i) = true
        cmp(i) = k
        while (stack.nonEmpty) {
          val v = stack.top
          var pushed = false
          for {
            u <- rg(v)
            if !used(u)
          } {
            used(u) = true
            cmp(u) = k
            stack = stack.push(u)
            pushed = true
          }
          if (!pushed) {
            stack = stack.pop
          }
        }
        k += 1
      }
      cmp
    }
  }

}

Measured memory_bytes: 512736