646815621 has 4 divisors (see below), whose sum is σ = 862420832. Its totient is φ = 431210412.

The previous prime is 646815619. The next prime is 646815641. The reversal of 646815621 is 126518646.

It is a happy number.

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 not a de Polignac number, because 646815621 - 2¹ = 646815619 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 646815621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (646815641) 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, 107802601 + ... + 107802606.

It is an arithmetic number, because the mean of its divisors is an integer number (215605208).

Almost surely, 2^646815621 is an apocalyptic number.

It is an amenable number.

646815621 is a deficient number, since it is larger than the sum of its proper divisors (215605211).

646815621 is a wasteful number, since it uses less digits than its factorization.

646815621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 215605210.

The product of its digits is 69120, while the sum is 39.

The square root of 646815621 is about 25432.5700824750. The cubic root of 646815621 is about 864.8222076592.

The spelling of 646815621 in words is "six hundred forty-six million, eight hundred fifteen thousand, six hundred twenty-one".