644721937 has 2 divisors, whose sum is σ = 644721938. Its totient is φ = 644721936.

The previous prime is 644721877. The next prime is 644721941. The reversal of 644721937 is 739127446.

644721937 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 458645056 + 186076881 = 21416^2 + 13641^2 .

It is a cyclic number.

It is not a de Polignac number, because 644721937 - 2²⁷ = 510504209 is a prime.

It is a super-3 number, since 3×644721937³ (a number of 27 digits) contains 333 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 644721893 and 644721902.

It is not a weakly prime, because it can be changed into another prime (644721037) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322360968 + 322360969.

It is an arithmetic number, because the mean of its divisors is an integer number (322360969).

Almost surely, 2^644721937 is an apocalyptic number.

It is an amenable number.

644721937 is a deficient number, since it is larger than the sum of its proper divisors (1).

644721937 is an equidigital number, since it uses as much as digits as its factorization.

644721937 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 254016, while the sum is 43.

The square root of 644721937 is about 25391.3752483004. The cubic root of 644721937 is about 863.8880818003. Note that the first 3 decimals are identical.

The spelling of 644721937 in words is "six hundred forty-four million, seven hundred twenty-one thousand, nine hundred thirty-seven".