21978839 has 16 divisors (see below), whose sum is σ = 24213600. Its totient is φ = 19869696.

The previous prime is 21978799. The next prime is 21978871. The reversal of 21978839 is 93887912.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21978839 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21978793 and 21978802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21978899) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 62087 + ... + 62439.

It is an arithmetic number, because the mean of its divisors is an integer number (1513350).

Almost surely, 2^21978839 is an apocalyptic number.

21978839 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

21978839 is a deficient number, since it is larger than the sum of its proper divisors (2234761).

21978839 is a wasteful number, since it uses less digits than its factorization.

21978839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 514.

The product of its digits is 217728, while the sum is 47.

The square root of 21978839 is about 4688.1594469472. The cubic root of 21978839 is about 280.1140649211.

The spelling of 21978839 in words is "twenty-one million, nine hundred seventy-eight thousand, eight hundred thirty-nine".