668723021 has 4 divisors (see below), whose sum is σ = 668774844. Its totient is φ = 668671200.

The previous prime is 668723017. The next prime is 668723059. The reversal of 668723021 is 120327866.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 489028996 + 179694025 = 22114^2 + 13405^2 .

It is a cyclic number.

It is not a de Polignac number, because 668723021 - 2² = 668723017 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668723621) 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, 10511 + ... + 38051.

It is an arithmetic number, because the mean of its divisors is an integer number (167193711).

Almost surely, 2^668723021 is an apocalyptic number.

It is an amenable number.

668723021 is a deficient number, since it is larger than the sum of its proper divisors (51823).

668723021 is a wasteful number, since it uses less digits than its factorization.

668723021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51822.

The product of its (nonzero) digits is 24192, while the sum is 35.

The square root of 668723021 is about 25859.6794450357. The cubic root of 668723021 is about 874.4777382986.

The spelling of 668723021 in words is "six hundred sixty-eight million, seven hundred twenty-three thousand, twenty-one".