644135843 has 4 divisors (see below), whose sum is σ = 693684768. Its totient is φ = 594586920.

The previous prime is 644135839. The next prime is 644135851. The reversal of 644135843 is 348531446.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 348531446 = 2 ⋅174265723.

It is a cyclic number.

It is not a de Polignac number, because 644135843 - 2² = 644135839 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 644135797 and 644135806.

It is not an unprimeable number, because it can be changed into a prime (644135873) 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, 24774443 + ... + 24774468.

It is an arithmetic number, because the mean of its divisors is an integer number (173421192).

Almost surely, 2^644135843 is an apocalyptic number.

644135843 is a deficient number, since it is larger than the sum of its proper divisors (49548925).

644135843 is a wasteful number, since it uses less digits than its factorization.

644135843 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49548924.

The product of its digits is 138240, while the sum is 38.

The square root of 644135843 is about 25379.8314218200. The cubic root of 644135843 is about 863.6262256958.

The spelling of 644135843 in words is "six hundred forty-four million, one hundred thirty-five thousand, eight hundred forty-three".