646181993 has 4 divisors (see below), whose sum is σ = 648220740. Its totient is φ = 644143248.

The previous prime is 646181959. The next prime is 646182037. The reversal of 646181993 is 399181646.

646181993 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 83685904 + 562496089 = 9148^2 + 23717^2 .

It is a cyclic number.

It is not a de Polignac number, because 646181993 - 2¹⁴ = 646165609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (646181923) 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, 1018898 + ... + 1019531.

It is an arithmetic number, because the mean of its divisors is an integer number (162055185).

Almost surely, 2^646181993 is an apocalyptic number.

It is an amenable number.

646181993 is a deficient number, since it is larger than the sum of its proper divisors (2038747).

646181993 is a wasteful number, since it uses less digits than its factorization.

646181993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2038746.

The product of its digits is 279936, while the sum is 47.

The square root of 646181993 is about 25420.1100115637. The cubic root of 646181993 is about 864.5397188119.

The spelling of 646181993 in words is "six hundred forty-six million, one hundred eighty-one thousand, nine hundred ninety-three".