645871 has 4 divisors (see below), whose sum is σ = 649144. Its totient is φ = 642600.

The previous prime is 645857. The next prime is 645877. The reversal of 645871 is 178546.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 178546 = 2 ⋅89273.

It is a cyclic number.

It is not a de Polignac number, because 645871 - 2⁵ = 645839 is a prime.

It is a super-3 number, since 3×645871³ = 808274000868333933, which contains 333 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 (645877) 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, 1320 + ... + 1741.

It is an arithmetic number, because the mean of its divisors is an integer number (162286).

2⁶⁴⁵⁸⁷¹ is an apocalyptic number.

645871 is a deficient number, since it is larger than the sum of its proper divisors (3273).

645871 is a wasteful number, since it uses less digits than its factorization.

645871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3272.

The product of its digits is 6720, while the sum is 31.

The square root of 645871 is about 803.6609981827. The cubic root of 645871 is about 86.4401001986.

The spelling of 645871 in words is "six hundred forty-five thousand, eight hundred seventy-one".