638466721 has 2 divisors, whose sum is σ = 638466722. Its totient is φ = 638466720.

The previous prime is 638466679. The next prime is 638466733. The reversal of 638466721 is 127664836.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 465912225 + 172554496 = 21585^2 + 13136^2 .

It is a cyclic number.

It is not a de Polignac number, because 638466721 - 2⁷ = 638466593 is a prime.

It is not a weakly prime, because it can be changed into another prime (638466791) 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, 319233360 + 319233361.

It is an arithmetic number, because the mean of its divisors is an integer number (319233361).

Almost surely, 2^638466721 is an apocalyptic number.

It is an amenable number.

638466721 is a deficient number, since it is larger than the sum of its proper divisors (1).

638466721 is an equidigital number, since it uses as much as digits as its factorization.

638466721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 290304, while the sum is 43.

The square root of 638466721 is about 25267.8990222773. The cubic root of 638466721 is about 861.0851278915.

The spelling of 638466721 in words is "six hundred thirty-eight million, four hundred sixty-six thousand, seven hundred twenty-one".