644997971 has 6 divisors (see below), whose sum is σ = 656118972. Its totient is φ = 634062380.

The previous prime is 644997943. The next prime is 644998007. The reversal of 644997971 is 179799446.

It is not a de Polignac number, because 644997971 - 2⁶ = 644997907 is a prime.

It is a super-4 number, since 4×644997971⁴ (a number of 36 digits) contains 4444 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644997931) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 89165 + ... + 96126.

It is an arithmetic number, because the mean of its divisors is an integer number (109353162).

Almost surely, 2^644997971 is an apocalyptic number.

644997971 is a deficient number, since it is larger than the sum of its proper divisors (11121001).

644997971 is an equidigital number, since it uses as much as digits as its factorization.

644997971 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 185409 (or 185350 counting only the distinct ones).

The product of its digits is 3429216, while the sum is 56.

The square root of 644997971 is about 25396.8102524707. The cubic root of 644997971 is about 864.0113537853.

The spelling of 644997971 in words is "six hundred forty-four million, nine hundred ninety-seven thousand, nine hundred seventy-one".