645658381 has 2 divisors, whose sum is σ = 645658382. Its totient is φ = 645658380.

The previous prime is 645658379. The next prime is 645658397. The reversal of 645658381 is 183856546.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 563302756 + 82355625 = 23734^2 + 9075^2 .

It is a cyclic number.

It is not a de Polignac number, because 645658381 - 2¹ = 645658379 is a prime.

It is a super-2 number, since 2×645658381² = 833749489911082322, which contains 22 as substring.

Together with 645658379, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645658781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322829190 + 322829191.

It is an arithmetic number, because the mean of its divisors is an integer number (322829191).

Almost surely, 2^645658381 is an apocalyptic number.

It is an amenable number.

645658381 is a deficient number, since it is larger than the sum of its proper divisors (1).

645658381 is an equidigital number, since it uses as much as digits as its factorization.

645658381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 691200, while the sum is 46.

The square root of 645658381 is about 25409.8087556754. The cubic root of 645658381 is about 864.3061387454.

The spelling of 645658381 in words is "six hundred forty-five million, six hundred fifty-eight thousand, three hundred eighty-one".