646379891 has 4 divisors (see below), whose sum is σ = 658575792. Its totient is φ = 634183992.

The previous prime is 646379873. The next prime is 646379893. The reversal of 646379891 is 198973646.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 198973646 = 2 ⋅99486823.

It is a cyclic number.

It is not a de Polignac number, because 646379891 - 2²² = 642185587 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (53), and also a Moran number because the ratio is a prime number: 12195847 = 646379891 / (6 + 4 + 6 + 3 + 7 + 9 + 8 + 9 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (646379893) 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, 6097871 + ... + 6097976.

It is an arithmetic number, because the mean of its divisors is an integer number (164643948).

Almost surely, 2^646379891 is an apocalyptic number.

646379891 is a deficient number, since it is larger than the sum of its proper divisors (12195901).

646379891 is a wasteful number, since it uses less digits than its factorization.

646379891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12195900.

The product of its digits is 1959552, while the sum is 53.

The square root of 646379891 is about 25424.0022616424. The cubic root of 646379891 is about 864.6279670248.

The spelling of 646379891 in words is "six hundred forty-six million, three hundred seventy-nine thousand, eight hundred ninety-one".