644217505 has 4 divisors (see below), whose sum is σ = 773061012. Its totient is φ = 515374000.

The previous prime is 644217503. The next prime is 644217527. The reversal of 644217505 is 505712446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 505712446 = 2 ⋅252856223.

It can be written as a sum of positive squares in 2 ways, for example, as 79869969 + 564347536 = 8937^2 + 23756^2 .

It is not a de Polignac number, because 644217505 - 2¹ = 644217503 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644217503) 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, 64421746 + ... + 64421755.

It is an arithmetic number, because the mean of its divisors is an integer number (193265253).

Almost surely, 2^644217505 is an apocalyptic number.

It is an amenable number.

644217505 is a deficient number, since it is larger than the sum of its proper divisors (128843507).

644217505 is a wasteful number, since it uses less digits than its factorization.

644217505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128843506.

The product of its (nonzero) digits is 33600, while the sum is 34.

The square root of 644217505 is about 25381.4401679653. The cubic root of 644217505 is about 863.6627203087.

The spelling of 644217505 in words is "six hundred forty-four million, two hundred seventeen thousand, five hundred five".