638909813 has 2 divisors, whose sum is σ = 638909814. Its totient is φ = 638909812.

The previous prime is 638909807. The next prime is 638909837. The reversal of 638909813 is 318909836.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 428572804 + 210337009 = 20702^2 + 14503^2 .

It is a cyclic number.

It is not a de Polignac number, because 638909813 - 2⁶ = 638909749 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638909863) 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, 319454906 + 319454907.

It is an arithmetic number, because the mean of its divisors is an integer number (319454907).

Almost surely, 2^638909813 is an apocalyptic number.

It is an amenable number.

638909813 is a deficient number, since it is larger than the sum of its proper divisors (1).

638909813 is an equidigital number, since it uses as much as digits as its factorization.

638909813 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 279936, while the sum is 47.

The square root of 638909813 is about 25276.6653852916. The cubic root of 638909813 is about 861.2842777667.

The spelling of 638909813 in words is "six hundred thirty-eight million, nine hundred nine thousand, eight hundred thirteen".