21978194 has 32 divisors (see below), whose sum is σ = 39398400. Its totient is φ = 8997120.

The previous prime is 21978181. The next prime is 21978217. The reversal of 21978194 is 49187912.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 38342 + ... + 38910.

It is an arithmetic number, because the mean of its divisors is an integer number (1231200).

Almost surely, 2^21978194 is an apocalyptic number.

21978194 is a deficient number, since it is larger than the sum of its proper divisors (17420206).

21978194 is a wasteful number, since it uses less digits than its factorization.

21978194 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 698.

The product of its digits is 36288, while the sum is 41.

The square root of 21978194 is about 4688.0906561200. The cubic root of 21978194 is about 280.1113247803. Note that the first 3 decimals are identical.

The spelling of 21978194 in words is "twenty-one million, nine hundred seventy-eight thousand, one hundred ninety-four".