1 program j01;
 2 const maxn=30086;mo=1000000007;
 3 var a:array[0..maxn]of longint;
 4     c:array[0..200,0..200]of int64;
 5     num:array[0..maxn]of longint;
 6     cnt,i,j,k,n,sp:longint;
 7     ans:int64;
 8     f:array[0..maxn,0..100,0..3]of int64;
 9 
10 procedure sort(l,r:longint);
11 var i,j,x,y:longint;
12 begin
13   i:=l;j:=r;x:=a[(i+j)div 2];
14   repeat
15     while a[i]<x do inc(i);
16     while x<a[j] do dec(j);
17     if i<=j then
18     begin
19       y:=a[i];a[i]:=a[j];a[j]:=y;
20       inc(i);dec(j);
21     end;
22   until i>j;
23   if i<r then sort(i,r);
24   if l<j then sort(l,j);
25 end;
26 
27 procedure pre;
28 var i:longint;
29 begin
30   sort(1,n);
31   cnt:=1;num[1]:=1;
32   for i:=2 to n do
33   begin
34     if a[i]-a[i-1]>1 then
35     begin
36       writeln(0);halt;
37     end;
38     if a[i]<>a[i-1] then inc(cnt);
39     inc(num[cnt]);
40   end;
41   c[0,0]:=1;
42   for i:=1 to 200 do
43   begin
44     c[i,0]:=1;
45     for j:=1 to i do c[i,j]:=(c[i-1,j]+c[i-1,j-1])mod mo;
46   end;
47 end;
48 
49 begin
50   readln(n);
51   for i:=1 to n do read(a[i]);
52   pre;
53   f[1,1,3]:=1;
54   for i:=1 to cnt-1 do
55   begin
56     for j:=1 to num[i] do
57     begin
58       sp:=num[i]-j;
59       if f[i,j,0]>0 then
60         for k:=1 to sp do
61           f[i+1,k,0]:=(f[i+1,k,0]+f[i,j,0]*c[sp,k]mod mo*c[num[i+1]-1,k-1]mod mo)mod mo;
62       if f[i,j,1]>0 then
63       begin
64         for k:=1 to sp do
65           f[i+1,k,0]:=(f[i+1,k,0]+f[i,j,1]*c[sp,k]mod mo*c[num[i+1]-1,k-1]mod mo)mod mo;
66         for k:=0 to sp do
67           f[i+1,k+1,1]:=(f[i+1,k+1,1]+f[i,j,1]*c[sp,k]mod mo*c[num[i+1]-1,k]mod mo)mod mo;
68       end;
69       if f[i,j,2]>0 then
70       begin
71         for k:=1 to sp do
72           f[i+1,k,0]:=(f[i+1,k,0]+f[i,j,2]*c[sp,k]mod mo*c[num[i+1]-1,k-1]mod mo)mod mo;
73         for k:=0 to sp do
74           f[i+1,k+1,2]:=(f[i+1,k+1,2]+f[i,j,2]*c[sp,k]mod mo*c[num[i+1]-1,k]mod mo)mod mo;
75       end;
76       if f[i,j,3]>0 then
77       begin
78         for k:=1 to sp do
79           f[i+1,k,0]:=(f[i+1,k,0]+f[i,j,3]*c[sp,k]mod mo*c[num[i+1]-1,k-1]mod mo)mod mo;
80         for k:=0 to sp do
81           f[i+1,k+1,1]:=(f[i+1,k+1,1]+f[i,j,3]*c[sp,k]mod mo*c[num[i+1]-1,k]mod mo)mod mo;
82         for k:=0 to sp do
83           f[i+1,k+1,2]:=(f[i+1,k+1,2]+f[i,j,3]*c[sp,k]mod mo*c[num[i+1]-1,k]mod mo)mod mo;
84         for k:=2 to sp+2 do
85           f[i+1,k,3]:=(f[i+1,k,3]+f[i,j,3]*c[sp,k-2]mod mo*c[num[i+1]-1,k-1]mod mo)mod mo;
86       end;
87     end;
88   end;
89   ans:=0;
90   for i:=1 to num[cnt] do
91     ans:=(ans+f[cnt,i,0]+f[cnt,i,1]+f[cnt,i,2]+f[cnt,i,3])mod mo;
92   writeln(ans);
93 end.