645523909 has 2 divisors, whose sum is σ = 645523910. Its totient is φ = 645523908.

The previous prime is 645523877. The next prime is 645523927. The reversal of 645523909 is 909325546.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 643890625 + 1633284 = 25375^2 + 1278^2 .

It is a cyclic number.

It is not a de Polignac number, because 645523909 - 2⁵ = 645523877 is a prime.

It is a super-2 number, since 2×645523909² = 833402234181280562, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645529909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322761954 + 322761955.

It is an arithmetic number, because the mean of its divisors is an integer number (322761955).

Almost surely, 2^645523909 is an apocalyptic number.

It is an amenable number.

645523909 is a deficient number, since it is larger than the sum of its proper divisors (1).

645523909 is an equidigital number, since it uses as much as digits as its factorization.

645523909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 291600, while the sum is 43.

The square root of 645523909 is about 25407.1625531069. The cubic root of 645523909 is about 864.2461312408.

The spelling of 645523909 in words is "six hundred forty-five million, five hundred twenty-three thousand, nine hundred nine".