1638489691 has 2 divisors, whose sum is σ = 1638489692. Its totient is φ = 1638489690.

The previous prime is 1638489679. The next prime is 1638489773. The reversal of 1638489691 is 1969848361.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1638489691 - 2⁵ = 1638489659 is a prime.

It is not a weakly prime, because it can be changed into another prime (1638489991) 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, 819244845 + 819244846.

It is an arithmetic number, because the mean of its divisors is an integer number (819244846).

Almost surely, 2^1638489691 is an apocalyptic number.

1638489691 is a deficient number, since it is larger than the sum of its proper divisors (1).

1638489691 is an equidigital number, since it uses as much as digits as its factorization.

1638489691 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2239488, while the sum is 55.

The square root of 1638489691 is about 40478.2619562649. The cubic root of 1638489691 is about 1178.9115911821.

The spelling of 1638489691 in words is "one billion, six hundred thirty-eight million, four hundred eighty-nine thousand, six hundred ninety-one".