1638239021 has 2 divisors, whose sum is σ = 1638239022. Its totient is φ = 1638239020.

The previous prime is 1638238991. The next prime is 1638239023. The reversal of 1638239021 is 1209328361.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1609132996 + 29106025 = 40114^2 + 5395^2 .

It is an emirp because it is prime and its reverse (1209328361) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1638239021 is a prime.

Together with 1638239023, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1638239023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 819119510 + 819119511.

It is an arithmetic number, because the mean of its divisors is an integer number (819119511).

Almost surely, 2^1638239021 is an apocalyptic number.

It is an amenable number.

1638239021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1638239021 is an equidigital number, since it uses as much as digits as its factorization.

1638239021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15552, while the sum is 35.

The square root of 1638239021 is about 40475.1654845289. The cubic root of 1638239021 is about 1178.8514681632.

The spelling of 1638239021 in words is "one billion, six hundred thirty-eight million, two hundred thirty-nine thousand, twenty-one".