21978188144639 has 4 divisors (see below), whose sum is σ = 22933761542256. Its totient is φ = 21022614747024.

The previous prime is 21978188144611. The next prime is 21978188144681. The reversal of 21978188144639 is 93644188187912.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21978188144639 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 (21978188144609) 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, 477786698774 + ... + 477786698819.

It is an arithmetic number, because the mean of its divisors is an integer number (5733440385564).

Almost surely, 2^{21978188144639} is an apocalyptic number.

21978188144639 is a deficient number, since it is larger than the sum of its proper divisors (955573397617).

21978188144639 is an equidigital number, since it uses as much as digits as its factorization.

21978188144639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 955573397616.

The product of its digits is 167215104, while the sum is 71.

The spelling of 21978188144639 in words is "twenty-one trillion, nine hundred seventy-eight billion, one hundred eighty-eight million, one hundred forty-four thousand, six hundred thirty-nine".