645181 has 4 divisors (see below), whose sum is σ = 646812. Its totient is φ = 643552.

The previous prime is 645179. The next prime is 645187. The reversal of 645181 is 181546.

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 511225 + 133956 = 715^2 + 366^2 .

It is a cyclic number.

It is not a de Polignac number, because 645181 - 2¹ = 645179 is a prime.

It is a super-2 number, since 2×645181² = 832517045522, 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 (645187) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 201 + ... + 1153.

It is an arithmetic number, because the mean of its divisors is an integer number (161703).

2⁶⁴⁵¹⁸¹ is an apocalyptic number.

It is an amenable number.

645181 is a deficient number, since it is larger than the sum of its proper divisors (1631).

645181 is an equidigital number, since it uses as much as digits as its factorization.

645181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1630.

The product of its digits is 960, while the sum is 25.

The square root of 645181 is about 803.2315979840. The cubic root of 645181 is about 86.4093071964.

The spelling of 645181 in words is "six hundred forty-five thousand, one hundred eighty-one".