644121431 has 4 divisors (see below), whose sum is σ = 644672664. Its totient is φ = 643570200.

The previous prime is 644121427. The next prime is 644121461. The reversal of 644121431 is 134121446.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 644121431 - 2² = 644121427 is a prime.

It is a super-2 number, since 2×644121431² = 829784835746975522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 644121431.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644121461) 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, 273860 + ... + 276201.

It is an arithmetic number, because the mean of its divisors is an integer number (161168166).

Almost surely, 2^644121431 is an apocalyptic number.

644121431 is a deficient number, since it is larger than the sum of its proper divisors (551233).

644121431 is a wasteful number, since it uses less digits than its factorization.

644121431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 551232.

The product of its digits is 2304, while the sum is 26.

The square root of 644121431 is about 25379.5474939960. The cubic root of 644121431 is about 863.6197846766.

Adding to 644121431 its reverse (134121446), we get a palindrome (778242877).

It can be divided in two parts, 6441 and 21431, that added together give a palindrome (27872).

The spelling of 644121431 in words is "six hundred forty-four million, one hundred twenty-one thousand, four hundred thirty-one".