668138421 has 8 divisors (see below), whose sum is σ = 892624320. Its totient is φ = 444539072.

The previous prime is 668138411. The next prime is 668138423. The reversal of 668138421 is 124831866.

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

It is a cyclic number.

It is not a de Polignac number, because 668138421 - 2⁶ = 668138357 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 668138421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668138423) 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, 219876 + ... + 222893.

It is an arithmetic number, because the mean of its divisors is an integer number (111578040).

Almost surely, 2^668138421 is an apocalyptic number.

It is an amenable number.

668138421 is a deficient number, since it is larger than the sum of its proper divisors (224485899).

668138421 is a wasteful number, since it uses less digits than its factorization.

668138421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 443275.

The product of its digits is 55296, while the sum is 39.

The square root of 668138421 is about 25848.3736625730. The cubic root of 668138421 is about 874.2228401758. Note that the first 3 decimals are identical.

The spelling of 668138421 in words is "six hundred sixty-eight million, one hundred thirty-eight thousand, four hundred twenty-one".