21642978 has 32 divisors (see below), whose sum is σ = 49959936. Its totient is φ = 6122448.

The previous prime is 21642953. The next prime is 21642979. The reversal of 21642978 is 87924612.

It is not an unprimeable number, because it can be changed into a prime (21642979) by changing a digit.

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, 1825 + ... + 6827.

It is an arithmetic number, because the mean of its divisors is an integer number (1561248).

Almost surely, 2^21642978 is an apocalyptic number.

21642978 is an abundant number, since it is smaller than the sum of its proper divisors (28316958).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21642978 is a wasteful number, since it uses less digits than its factorization.

21642978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5118.

The product of its digits is 48384, while the sum is 39.

The square root of 21642978 is about 4652.2014143844. The cubic root of 21642978 is about 278.6799170941.

The spelling of 21642978 in words is "twenty-one million, six hundred forty-two thousand, nine hundred seventy-eight".