638221818 has 32 divisors (see below), whose sum is σ = 1446984000. Its totient is φ = 186039936.

The previous prime is 638221811. The next prime is 638221823. The reversal of 638221818 is 818122836.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is not an unprimeable number, because it can be changed into a prime (638221811) 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 in 15 ways as a sum of consecutive naturals, for example, 213843 + ... + 216806.

It is an arithmetic number, because the mean of its divisors is an integer number (45218250).

Almost surely, 2^638221818 is an apocalyptic number.

638221818 is an abundant number, since it is smaller than the sum of its proper divisors (808762182).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

638221818 is a wasteful number, since it uses less digits than its factorization.

638221818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 430686.

The product of its digits is 36864, while the sum is 39.

The square root of 638221818 is about 25263.0524283983. The cubic root of 638221818 is about 860.9750154960.

The spelling of 638221818 in words is "six hundred thirty-eight million, two hundred twenty-one thousand, eight hundred eighteen".