644540051 has 4 divisors (see below), whose sum is σ = 666765600. Its totient is φ = 622314504.

The previous prime is 644540033. The next prime is 644540077. The reversal of 644540051 is 150045446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 150045446 = 2 ⋅75022723.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644540051 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29), and also a Moran number because the ratio is a prime number: 22225519 = 644540051 / (6 + 4 + 4 + 5 + 4 + 0 + 0 + 5 + 1).

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 644539996 and 644540023.

It is not an unprimeable number, because it can be changed into a prime (644540011) 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, 11112731 + ... + 11112788.

It is an arithmetic number, because the mean of its divisors is an integer number (166691400).

Almost surely, 2^644540051 is an apocalyptic number.

644540051 is a deficient number, since it is larger than the sum of its proper divisors (22225549).

644540051 is a wasteful number, since it uses less digits than its factorization.

644540051 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22225548.

The product of its (nonzero) digits is 9600, while the sum is 29.

The square root of 644540051 is about 25387.7933464096. The cubic root of 644540051 is about 863.8068354432.

Adding to 644540051 its reverse (150045446), we get a palindrome (794585497).

The spelling of 644540051 in words is "six hundred forty-four million, five hundred forty thousand, fifty-one".