1666128215 has 4 divisors (see below), whose sum is σ = 1999353864. Its totient is φ = 1332902568.

The previous prime is 1666128209. The next prime is 1666128223. The reversal of 1666128215 is 5128216661.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5128216661 = 97 ⋅52868213.

It is a cyclic number.

It is not a de Polignac number, because 1666128215 - 2⁶ = 1666128151 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 166612817 + ... + 166612826.

It is an arithmetic number, because the mean of its divisors is an integer number (499838466).

Almost surely, 2^1666128215 is an apocalyptic number.

1666128215 is a deficient number, since it is larger than the sum of its proper divisors (333225649).

1666128215 is an equidigital number, since it uses as much as digits as its factorization.

1666128215 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 333225648.

The product of its digits is 34560, while the sum is 38.

The square root of 1666128215 is about 40818.2338544920. The cubic root of 1666128215 is about 1185.5034067357.

The spelling of 1666128215 in words is "one billion, six hundred sixty-six million, one hundred twenty-eight thousand, two hundred fifteen".