1638991 has 2 divisors, whose sum is σ = 1638992. Its totient is φ = 1638990.

The previous prime is 1638983. The next prime is 1639019. The reversal of 1638991 is 1998361.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1638991 - 2³ = 1638983 is a prime.

1638991 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 1638991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1638191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 819495 + 819496.

It is an arithmetic number, because the mean of its divisors is an integer number (819496).

2^1638991 is an apocalyptic number.

1638991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1638991 is an equidigital number, since it uses as much as digits as its factorization.

1638991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11664, while the sum is 37.

The square root of 1638991 is about 1280.2308385600. The cubic root of 1638991 is about 117.9031811393.

The spelling of 1638991 in words is "one million, six hundred thirty-eight thousand, nine hundred ninety-one".