void main() {
	auto N = readAs!long;
	auto A = readAs!(long[]);
	long[][long] m;
	foreach(i, v; A) m[v] ~= i;
	auto arr = A.dup.sort();
	debug arr.writeln;
	ulong cnt;
	debug m.writeln;
	alias Pair = Tuple!(long, "a", long, "b");
	auto rbt = redBlackTree!Pair;

	foreach(v; arr) {
		auto p = m[v];
		long[] bigarr;
		foreach(v2; m.keys.filter!(a => a >= v).array) bigarr ~= m[v2];
		foreach(i; p) {
			foreach(j; bigarr) {
				debug writefln("i: %d, j: %d", i, j);
				if(A[j] + A[i] == abs(j - i)) {
					if(!rbt.insert(Pair(i, j)) || !rbt.insert(Pair(j, i))) continue;
					cnt++;
					debug writefln("ok: %d+%d=|%d-%d|", A[j], A[i], j, i);
				}
			}
		}
	}
	cnt.writeln;
}

// ===================================

import std.stdio;
import std.string;
import std.functional;
import std.algorithm;
import std.range;
import std.traits;
import std.math;
import std.container;
import std.bigint;
import std.numeric;
import std.conv;
import std.typecons;
import std.uni;
import std.ascii;
import std.bitmanip;
import core.bitop;

T readAs(T)() if (isBasicType!T) {
	return readln.chomp.to!T;
}
T readAs(T)() if (isArray!T) {
	return readln.split.to!T;
}

T[][] readMatrix(T)(uint height, uint width) if (!isSomeChar!T) {
	auto res = new T[][](height, width);
	foreach(i; 0..height) {
		res[i] = readAs!(T[]);
	}
	return res;
}

T[][] readMatrix(T)(uint height, uint width) if (isSomeChar!T) {
	auto res = new T[][](height, width);
	foreach(i; 0..height) {
		auto s = rs;
		foreach(j; 0..width) res[i][j] = s[j].to!T;
	}
	return res;
}

int ri() {
	return readAs!int;
}

double rd() {
	return readAs!double;
}

string rs() {
	return readln.chomp;
}