644667520 has 192 divisors, whose sum is σ = 1827572760. Its totient is φ = 216760320.

The previous prime is 644667509. The next prime is 644667521. The reversal of 644667520 is 25766446.

It can be written as a sum of positive squares in 4 ways, for example, as 258309184 + 386358336 = 16072^2 + 19656^2 .

It is a super-2 number, since 2×644667520² = 831192422685900800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644667521) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1912792 + ... + 1913128.

Almost surely, 2^644667520 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644667520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (913786380).

644667520 is an abundant number, since it is smaller than the sum of its proper divisors (1182905240).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644667520 is a wasteful number, since it uses less digits than its factorization.

644667520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 431 (or 412 counting only the distinct ones).

The product of its (nonzero) digits is 241920, while the sum is 40.

The square root of 644667520 is about 25390.3036610435. The cubic root of 644667520 is about 863.8637759625.

The spelling of 644667520 in words is "six hundred forty-four million, six hundred sixty-seven thousand, five hundred twenty".