644180561 has 4 divisors (see below), whose sum is σ = 659892324. Its totient is φ = 628468800.

The previous prime is 644180521. The next prime is 644180587. The reversal of 644180561 is 165081446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165081446 = 2 ⋅82540723.

It can be written as a sum of positive squares in 2 ways, for example, as 350400961 + 293779600 = 18719^2 + 17140^2 .

It is a cyclic number.

It is not a de Polignac number, because 644180561 - 2¹⁰ = 644179537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644180501) 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, 7855820 + ... + 7855901.

It is an arithmetic number, because the mean of its divisors is an integer number (164973081).

Almost surely, 2^644180561 is an apocalyptic number.

It is an amenable number.

644180561 is a deficient number, since it is larger than the sum of its proper divisors (15711763).

644180561 is a wasteful number, since it uses less digits than its factorization.

644180561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15711762.

The product of its (nonzero) digits is 23040, while the sum is 35.

The square root of 644180561 is about 25380.7123816492. The cubic root of 644180561 is about 863.6462104782.

The spelling of 644180561 in words is "six hundred forty-four million, one hundred eighty thousand, five hundred sixty-one".