645918181 has 2 divisors, whose sum is σ = 645918182. Its totient is φ = 645918180.

The previous prime is 645918149. The next prime is 645918193. The reversal of 645918181 is 181819546.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 639837025 + 6081156 = 25295^2 + 2466^2 .

It is a cyclic number.

It is not a de Polignac number, because 645918181 - 2⁵ = 645918149 is a prime.

It is a super-2 number, since 2×645918181² = 834420593092697522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645918101) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322959090 + 322959091.

It is an arithmetic number, because the mean of its divisors is an integer number (322959091).

Almost surely, 2^645918181 is an apocalyptic number.

It is an amenable number.

645918181 is a deficient number, since it is larger than the sum of its proper divisors (1).

645918181 is an equidigital number, since it uses as much as digits as its factorization.

645918181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 69120, while the sum is 43.

The square root of 645918181 is about 25414.9204405601. The cubic root of 645918181 is about 864.4220496928.

The spelling of 645918181 in words is "six hundred forty-five million, nine hundred eighteen thousand, one hundred eighty-one".