1638821 has 2 divisors, whose sum is σ = 1638822. Its totient is φ = 1638820.

The previous prime is 1638809. The next prime is 1638869. The reversal of 1638821 is 1288361.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1612900 + 25921 = 1270^2 + 161^2 .

It is an emirp because it is prime and its reverse (1288361) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1638821 - 2¹⁴ = 1622437 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a plaindrome in base 15.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1638121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 819410 + 819411.

It is an arithmetic number, because the mean of its divisors is an integer number (819411).

2^1638821 is an apocalyptic number.

It is an amenable number.

1638821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1638821 is an equidigital number, since it uses as much as digits as its factorization.

1638821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2304, while the sum is 29.

The square root of 1638821 is about 1280.1644425620. The cubic root of 1638821 is about 117.8991045999.

The spelling of 1638821 in words is "one million, six hundred thirty-eight thousand, eight hundred twenty-one".