666739921 has 4 divisors (see below), whose sum is σ = 666792000. Its totient is φ = 666687844.

The previous prime is 666739901. The next prime is 666739987. The reversal of 666739921 is 129937666.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 666739921 - 2¹³ = 666731729 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (666739901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7980 + ... + 37378.

It is an arithmetic number, because the mean of its divisors is an integer number (166698000).

Almost surely, 2^666739921 is an apocalyptic number.

It is an amenable number.

666739921 is a deficient number, since it is larger than the sum of its proper divisors (52079).

666739921 is a wasteful number, since it uses less digits than its factorization.

666739921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52078.

The product of its digits is 734832, while the sum is 49.

The square root of 666739921 is about 25821.3074998150. The cubic root of 666739921 is about 873.6124603417.

The spelling of 666739921 in words is "six hundred sixty-six million, seven hundred thirty-nine thousand, nine hundred twenty-one".