644640424440 has 32 divisors (see below), whose sum is σ = 1933921273680. Its totient is φ = 171904113152.

The previous prime is 644640424433. The next prime is 644640424447. The reversal of 644640424440 is 44424046446.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (644640424433) and next prime (644640424447).

It is a super-2 number, since 2×644640424440² (a number of 24 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 644640424392 and 644640424401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644640424447) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2686001649 + ... + 2686001888.

Almost surely, 2^644640424440 is an apocalyptic number.

644640424440 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644640424440 is an abundant number, since it is smaller than the sum of its proper divisors (1289280849240).

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

644640424440 is a wasteful number, since it uses less digits than its factorization.

644640424440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5372003551 (or 5372003547 counting only the distinct ones).

The product of its (nonzero) digits is 1179648, while the sum is 42.

The spelling of 644640424440 in words is "six hundred forty-four billion, six hundred forty million, four hundred twenty-four thousand, four hundred forty".