639925409 has 2 divisors, whose sum is σ = 639925410. Its totient is φ = 639925408.

The previous prime is 639925369. The next prime is 639925411. The reversal of 639925409 is 904529936.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 381616225 + 258309184 = 19535^2 + 16072^2 .

It is a cyclic number.

It is not a de Polignac number, because 639925409 - 2¹⁶ = 639859873 is a prime.

Together with 639925411, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (639925309) 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, 319962704 + 319962705.

It is an arithmetic number, because the mean of its divisors is an integer number (319962705).

Almost surely, 2^639925409 is an apocalyptic number.

It is an amenable number.

639925409 is a deficient number, since it is larger than the sum of its proper divisors (1).

639925409 is an equidigital number, since it uses as much as digits as its factorization.

639925409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 524880, while the sum is 47.

The square root of 639925409 is about 25296.7470043087. The cubic root of 639925409 is about 861.7403952458.

The spelling of 639925409 in words is "six hundred thirty-nine million, nine hundred twenty-five thousand, four hundred nine".