1638470921 has 2 divisors, whose sum is σ = 1638470922. Its totient is φ = 1638470920.

The previous prime is 1638470857. The next prime is 1638470927. The reversal of 1638470921 is 1290748361.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1578949696 + 59521225 = 39736^2 + 7715^2 .

It is a cyclic number.

It is not a de Polignac number, because 1638470921 - 2⁶ = 1638470857 is a prime.

It is not a weakly prime, because it can be changed into another prime (1638470927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 819235460 + 819235461.

It is an arithmetic number, because the mean of its divisors is an integer number (819235461).

Almost surely, 2^1638470921 is an apocalyptic number.

It is an amenable number.

1638470921 is a deficient number, since it is larger than the sum of its proper divisors (1).

1638470921 is an equidigital number, since it uses as much as digits as its factorization.

1638470921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 72576, while the sum is 41.

The square root of 1638470921 is about 40478.0301027607. The cubic root of 1638470921 is about 1178.9070894235.

The spelling of 1638470921 in words is "one billion, six hundred thirty-eight million, four hundred seventy thousand, nine hundred twenty-one".