644431505 has 24 divisors (see below), whose sum is σ = 799775208. Its totient is φ = 498308096.

The previous prime is 644431499. The next prime is 644431537. The reversal of 644431505 is 505134446.

644431505 is digitally balanced in base 2 and base 6, because in such bases it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 92698384 + 551733121 = 9628^2 + 23489^2 .

It is not a de Polignac number, because 644431505 - 2²² = 640237201 is a prime.

It is a super-3 number, since 3×644431505³ (a number of 27 digits) contains 333 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1825409 + ... + 1825761.

It is an arithmetic number, because the mean of its divisors is an integer number (33323967).

Almost surely, 2^644431505 is an apocalyptic number.

It is an amenable number.

644431505 is a deficient number, since it is larger than the sum of its proper divisors (155343703).

644431505 is an equidigital number, since it uses as much as digits as its factorization.

644431505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 577 (or 494 counting only the distinct ones).

The product of its (nonzero) digits is 28800, while the sum is 32.

The square root of 644431505 is about 25385.6554967564. The cubic root of 644431505 is about 863.7583419268.

The spelling of 644431505 in words is "six hundred forty-four million, four hundred thirty-one thousand, five hundred five".