1638404921 has 2 divisors, whose sum is σ = 1638404922. Its totient is φ = 1638404920.

The previous prime is 1638404899. The next prime is 1638404939. The reversal of 1638404921 is 1294048361.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1581175696 + 57229225 = 39764^2 + 7565^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1638404921 is a prime.

It is not a weakly prime, because it can be changed into another prime (1638404821) 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, 819202460 + 819202461.

It is an arithmetic number, because the mean of its divisors is an integer number (819202461).

Almost surely, 2^1638404921 is an apocalyptic number.

It is an amenable number.

1638404921 is a deficient number, since it is larger than the sum of its proper divisors (1).

1638404921 is an equidigital number, since it uses as much as digits as its factorization.

1638404921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 41472, while the sum is 38.

The square root of 1638404921 is about 40477.2148374860. The cubic root of 1638404921 is about 1178.8912598449.

The spelling of 1638404921 in words is "one billion, six hundred thirty-eight million, four hundred four thousand, nine hundred twenty-one".