N=int(input())
A=list(map(int,input().split()))

LIST=[[] for i in range(2001)]

for i in range(N):
    LIST[A[i]].append(i)

ANS=0

for k in range(1,2001):
    DP=[[0,0,0] for i in range(N)]
    for i in range(N):
        a=A[i]

        if 1<=a+k+10<=2000:
            for j in LIST[a+k+10]:
                if j>i:
                    DP[j][1]+=1

        if 1<=a-k<=2000:
            if DP[i][1]!=0:
                for j in LIST[a-k]:
                    if j>i:
                        DP[j][2]+=DP[i][1]

        if 1<=a+k+1<=2000:
            if DP[i][2]!=0:
                for j in LIST[a+k+1]:
                    if j>i:
                        ANS+=DP[i][2]

print(ANS)