644121240 has 64 divisors (see below), whose sum is σ = 2208418560. Its totient is φ = 147227520.

The previous prime is 644121239. The next prime is 644121253. The reversal of 644121240 is 42121446.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 644121240.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 382566 + ... + 384245.

It is an arithmetic number, because the mean of its divisors is an integer number (34506540).

Almost surely, 2^644121240 is an apocalyptic number.

644121240 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644121240 is an abundant number, since it is smaller than the sum of its proper divisors (1564297320).

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

644121240 is a wasteful number, since it uses less digits than its factorization.

644121240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 766832 (or 766828 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 24.

The square root of 644121240 is about 25379.5437311233. The cubic root of 644121240 is about 863.6196993141.

Adding to 644121240 its reverse (42121446), we get a palindrome (686242686).

The spelling of 644121240 in words is "six hundred forty-four million, one hundred twenty-one thousand, two hundred forty".