import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(1000005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# md = 10**9+7
md = 998244353

def solve(k):
    dp=[[0]*2005 for _ in range(4)]
    for a in aa:
        if a-k-1>0:dp[3][a]+=dp[2][a-k-1]
        if a+k<=2000:dp[2][a]+=dp[1][a+k]
        if a-k-10>0:dp[1][a]+=dp[0][a-k-10]
        dp[0][a]+=1
    return sum(dp[3])

n=II()
aa=LI()
ans=0
for k in range(1,2000):
    ans+=solve(k)
print(ans)