644073220261 has 4 divisors (see below), whose sum is σ = 644780217024. Its totient is φ = 643366223500.

The previous prime is 644073220249. The next prime is 644073220303. The reversal of 644073220261 is 162022370446.

644073220261 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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, and also an emirpimes, since its reverse is a distinct semiprime: 162022370446 = 2 ⋅81011185223.

It is a cyclic number.

It is not a de Polignac number, because 644073220261 - 2⁹ = 644073219749 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 644073220261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644073200261) 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, 353497015 + ... + 353498836.

It is an arithmetic number, because the mean of its divisors is an integer number (161195054256).

Almost surely, 2^644073220261 is an apocalyptic number.

It is an amenable number.

644073220261 is a deficient number, since it is larger than the sum of its proper divisors (706996763).

644073220261 is an equidigital number, since it uses as much as digits as its factorization.

644073220261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 706996762.

The product of its (nonzero) digits is 96768, while the sum is 37.

The spelling of 644073220261 in words is "six hundred forty-four billion, seventy-three million, two hundred twenty thousand, two hundred sixty-one".