1638448391 has 4 divisors (see below), whose sum is σ = 1646682000. Its totient is φ = 1630214784.

The previous prime is 1638448367. The next prime is 1638448403. The reversal of 1638448391 is 1938448361.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1938448361 = 103 ⋅18819887.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1638448391 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1638448891) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4116506 + ... + 4116903.

It is an arithmetic number, because the mean of its divisors is an integer number (411670500).

Almost surely, 2^1638448391 is an apocalyptic number.

1638448391 is a deficient number, since it is larger than the sum of its proper divisors (8233609).

1638448391 is an equidigital number, since it uses as much as digits as its factorization.

1638448391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8233608.

The product of its digits is 497664, while the sum is 47.

The square root of 1638448391 is about 40477.7518026879. The cubic root of 1638448391 is about 1178.9016858288.

The spelling of 1638448391 in words is "one billion, six hundred thirty-eight million, four hundred forty-eight thousand, three hundred ninety-one".