645581 has 2 divisors, whose sum is σ = 645582. Its totient is φ = 645580.

The previous prime is 645577. The next prime is 645583. The reversal of 645581 is 185546.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 477481 + 168100 = 691^2 + 410^2 .

It is a cyclic number.

It is not a de Polignac number, because 645581 - 2² = 645577 is a prime.

It is a super-2 number, since 2×645581² = 833549655122, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 645583, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 645581.

It is not a weakly prime, because it can be changed into another prime (645583) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322790 + 322791.

It is an arithmetic number, because the mean of its divisors is an integer number (322791).

2⁶⁴⁵⁵⁸¹ is an apocalyptic number.

It is an amenable number.

645581 is a deficient number, since it is larger than the sum of its proper divisors (1).

645581 is an equidigital number, since it uses as much as digits as its factorization.

645581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4800, while the sum is 29.

The square root of 645581 is about 803.4805535917. The cubic root of 645581 is about 86.4271608852.

The spelling of 645581 in words is "six hundred forty-five thousand, five hundred eighty-one".