66839921 has 4 divisors (see below), whose sum is σ = 67176000. Its totient is φ = 66503844.

The previous prime is 66839917. The next prime is 66839959. The reversal of 66839921 is 12993866.

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 66839921 - 2² = 66839917 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66839221) 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, 167741 + ... + 168138.

It is an arithmetic number, because the mean of its divisors is an integer number (16794000).

Almost surely, 2^66839921 is an apocalyptic number.

It is an amenable number.

66839921 is a deficient number, since it is larger than the sum of its proper divisors (336079).

66839921 is a wasteful number, since it uses less digits than its factorization.

66839921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 336078.

The product of its digits is 139968, while the sum is 44.

The square root of 66839921 is about 8175.5685429210. The cubic root of 66839921 is about 405.8310851444.

The spelling of 66839921 in words is "sixty-six million, eight hundred thirty-nine thousand, nine hundred twenty-one".