I,R=input,range
N=I()
A=list(map(int,I().split()))
c=0
L=R(1,2001)
for k in L:
	D=[[0]*4for a in R(4001)]
	for a in A:D[a]=[D[a][0]+1,D[a][1]+D[a-k-10][0],D[a][2]+D[a+k][1],D[a][3]+D[a-k-1][2]]
	c+=sum(D[a][3]for a in L)
print(c)