Any optimal approach for this?\nQuestion: count all the pairs with indices i<=j whose sum is a power of 2.\n\n```\ndef pairSummingToPowerOfTwo(a):\n    \n    if len(a)==1 and (a[0] and (not(a[0] & (a[0] - 1))) ):\n        return 1\n    \n    count  = 0\n    for i in range(len(a)):\n        for j in range(i, len(a)):\n\n            sum = a[i] + a[j]\n            if (sum and (not(sum & (sum - 1)))) == True:\n                count += 1\n                        \n    return count\n            \n            \n```

Any optimal approach for this?\nQuestion: count all the pairs with indices i<=j whose sum is a power of 2.\n\n\ndef pairSummingToPowerOfTwo(a):\n    \n    if le