1664728421 has 8 divisors (see below), whose sum is σ = 1672881600. Its totient is φ = 1656594720.

The previous prime is 1664728411. The next prime is 1664728433. The reversal of 1664728421 is 1248274661.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1664728421 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1664728411) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 183920 + ... + 192758.

It is an arithmetic number, because the mean of its divisors is an integer number (209110200).

Almost surely, 2^1664728421 is an apocalyptic number.

It is an amenable number.

1664728421 is a deficient number, since it is larger than the sum of its proper divisors (8153179).

1664728421 is an equidigital number, since it uses as much as digits as its factorization.

1664728421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9739.

The product of its digits is 129024, while the sum is 41.

The square root of 1664728421 is about 40801.0835762973. The cubic root of 1664728421 is about 1185.1713143456.

The spelling of 1664728421 in words is "one billion, six hundred sixty-four million, seven hundred twenty-eight thousand, four hundred twenty-one".