645871397 has 4 divisors (see below), whose sum is σ = 645944460. Its totient is φ = 645798336.

The previous prime is 645871381. The next prime is 645871399. The reversal of 645871397 is 793178546.

It is a Cunningham number, because it is equal to 25414²+1.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 575328196 + 70543201 = 23986^2 + 8399^2 .

It is a cyclic number.

It is not a de Polignac number, because 645871397 - 2⁴ = 645871381 is a prime.

It is a super-2 number, since 2×645871397² = 834299722925463218, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645871399) 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, 21098 + ... + 41675.

It is an arithmetic number, because the mean of its divisors is an integer number (161486115).

Almost surely, 2^645871397 is an apocalyptic number.

It is an amenable number.

645871397 is a deficient number, since it is larger than the sum of its proper divisors (73063).

645871397 is a wasteful number, since it uses less digits than its factorization.

645871397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 73062.

The product of its digits is 1270080, while the sum is 50.

The square root of 645871397 is about 25414.0000196742. Note that the first 4 decimals coincide. The cubic root of 645871397 is about 864.4011790940.

The spelling of 645871397 in words is "six hundred forty-five million, eight hundred seventy-one thousand, three hundred ninety-seven".