645308921 has 2 divisors, whose sum is σ = 645308922. Its totient is φ = 645308920.

The previous prime is 645308891. The next prime is 645308941. The reversal of 645308921 is 129803546.

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., 347263225 + 298045696 = 18635^2 + 17264^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-645308921 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (645308941) 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, 322654460 + 322654461.

It is an arithmetic number, because the mean of its divisors is an integer number (322654461).

Almost surely, 2^645308921 is an apocalyptic number.

It is an amenable number.

645308921 is a deficient number, since it is larger than the sum of its proper divisors (1).

645308921 is an equidigital number, since it uses as much as digits as its factorization.

645308921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 51840, while the sum is 38.

The square root of 645308921 is about 25402.9313465986. The cubic root of 645308921 is about 864.1501765311.

The spelling of 645308921 in words is "six hundred forty-five million, three hundred eight thousand, nine hundred twenty-one".