644633402505621 has 16 divisors (see below), whose sum is σ = 862801010924160. Its totient is φ = 428110780092480.

The previous prime is 644633402505619. The next prime is 644633402505623. The reversal of 644633402505621 is 126505204336446.

It is an interprime number because it is at equal distance from previous prime (644633402505619) and next prime (644633402505623).

It is not a de Polignac number, because 644633402505621 - 2¹ = 644633402505619 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644633402505623) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 21168411 + ... + 41681751.

It is an arithmetic number, because the mean of its divisors is an integer number (53925063182760).

Almost surely, 2^{644633402505621} is an apocalyptic number.

It is an amenable number.

644633402505621 is a deficient number, since it is larger than the sum of its proper divisors (218167608418539).

644633402505621 is a wasteful number, since it uses less digits than its factorization.

644633402505621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20553436.

The product of its (nonzero) digits is 12441600, while the sum is 51.

The spelling of 644633402505621 in words is "six hundred forty-four trillion, six hundred thirty-three billion, four hundred two million, five hundred five thousand, six hundred twenty-one".