644105331278 has 4 divisors (see below), whose sum is σ = 966157996920. Its totient is φ = 322052665638.

The previous prime is 644105331277. The next prime is 644105331299. The reversal of 644105331278 is 872133501446.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a super-2 number, since 2×644105331278² (a number of 24 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644105331277) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 161026332818 + ... + 161026332821.

It is an arithmetic number, because the mean of its divisors is an integer number (241539499230).

Almost surely, 2^644105331278 is an apocalyptic number.

644105331278 is a deficient number, since it is larger than the sum of its proper divisors (322052665642).

644105331278 is a wasteful number, since it uses less digits than its factorization.

644105331278 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 322052665641.

The product of its (nonzero) digits is 483840, while the sum is 44.

The spelling of 644105331278 in words is "six hundred forty-four billion, one hundred five million, three hundred thirty-one thousand, two hundred seventy-eight".