SOURCE

arr = [1, 2, 5, 6, 7];
for (let value of arr) {
  for (let val of arr) {
    if (val == value) {
      continue;
    }
    sum = value + val;
    if (sum != value && sum != val && arr.includes(sum)) {
      console.log(sum, value, val)
    }
  }
}