642809 has 2 divisors, whose sum is σ = 642810. Its totient is φ = 642808.

The previous prime is 642799. The next prime is 642833. The reversal of 642809 is 908246.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 640000 + 2809 = 800^2 + 53^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-642809 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 642809.

It is not a weakly prime, because it can be changed into another prime (642869) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321404 + 321405.

It is an arithmetic number, because the mean of its divisors is an integer number (321405).

2⁶⁴²⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

642809 is a deficient number, since it is larger than the sum of its proper divisors (1).

642809 is an equidigital number, since it uses as much as digits as its factorization.

642809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 642809 is about 801.7537028290. The cubic root of 642809 is about 86.3032829065.

It can be divided in two parts, 64 and 2809, that multiplied together give a square (179776 = 424²).

The spelling of 642809 in words is "six hundred forty-two thousand, eight hundred nine".