645405989 has 2 divisors, whose sum is σ = 645405990. Its totient is φ = 645405988.

The previous prime is 645405973. The next prime is 645405997. The reversal of 645405989 is 989504546.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 634183489 + 11222500 = 25183^2 + 3350^2 .

It is a cyclic number.

It is not a de Polignac number, because 645405989 - 2⁴ = 645405973 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645405949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322702994 + 322702995.

It is an arithmetic number, because the mean of its divisors is an integer number (322702995).

Almost surely, 2^645405989 is an apocalyptic number.

It is an amenable number.

645405989 is a deficient number, since it is larger than the sum of its proper divisors (1).

645405989 is an equidigital number, since it uses as much as digits as its factorization.

645405989 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1555200, while the sum is 50.

The square root of 645405989 is about 25404.8418416647. The cubic root of 645405989 is about 864.1935031308.

The spelling of 645405989 in words is "six hundred forty-five million, four hundred five thousand, nine hundred eighty-nine".