644973841 has 4 divisors (see below), whose sum is σ = 645826612. Its totient is φ = 644121072.

The previous prime is 644973821. The next prime is 644973877. The reversal of 644973841 is 148379446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 148379446 = 2 ⋅74189723.

It can be written as a sum of positive squares in 2 ways, for example, as 335073025 + 309900816 = 18305^2 + 17604^2 .

It is a cyclic number.

It is not a de Polignac number, because 644973841 - 2¹¹ = 644971793 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 644973791 and 644973800.

It is not an unprimeable number, because it can be changed into a prime (644973821) 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, 425250 + ... + 426763.

It is an arithmetic number, because the mean of its divisors is an integer number (161456653).

Almost surely, 2^644973841 is an apocalyptic number.

It is an amenable number.

644973841 is a deficient number, since it is larger than the sum of its proper divisors (852771).

644973841 is an equidigital number, since it uses as much as digits as its factorization.

644973841 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 852770.

The product of its digits is 580608, while the sum is 46.

The square root of 644973841 is about 25396.3351883692. The cubic root of 644973841 is about 864.0005791498. Note that the first 3 decimals are identical.

The spelling of 644973841 in words is "six hundred forty-four million, nine hundred seventy-three thousand, eight hundred forty-one".