21208978 has 32 divisors (see below), whose sum is σ = 38845440. Its totient is φ = 8482320.

The previous prime is 21208969. The next prime is 21208981. The reversal of 21208978 is 87980212.

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, 18325 + ... + 19447.

It is an arithmetic number, because the mean of its divisors is an integer number (1213920).

Almost surely, 2^21208978 is an apocalyptic number.

21208978 is a deficient number, since it is larger than the sum of its proper divisors (17636462).

21208978 is a wasteful number, since it uses less digits than its factorization.

21208978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1222.

The product of its (nonzero) digits is 16128, while the sum is 37.

The square root of 21208978 is about 4605.3206185889. The cubic root of 21208978 is about 276.8045644079.

The spelling of 21208978 in words is "twenty-one million, two hundred eight thousand, nine hundred seventy-eight".