1664793721 has 4 divisors (see below), whose sum is σ = 1700214912. Its totient is φ = 1629372532.

The previous prime is 1664793709. The next prime is 1664793727. The reversal of 1664793721 is 1273974661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1664793721 - 2⁹ = 1664793209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1664793727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17710525 + ... + 17710618.

It is an arithmetic number, because the mean of its divisors is an integer number (425053728).

Almost surely, 2^1664793721 is an apocalyptic number.

It is an amenable number.

1664793721 is a deficient number, since it is larger than the sum of its proper divisors (35421191).

1664793721 is an equidigital number, since it uses as much as digits as its factorization.

1664793721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35421190.

The product of its digits is 381024, while the sum is 46.

The square root of 1664793721 is about 40801.8837922957. The cubic root of 1664793721 is about 1185.1868105018.

The spelling of 1664793721 in words is "one billion, six hundred sixty-four million, seven hundred ninety-three thousand, seven hundred twenty-one".