21105978 has 32 divisors (see below), whose sum is σ = 44416512. Its totient is φ = 6676800.

The previous prime is 21105977. The next prime is 21106037. The reversal of 21105978 is 87950112.

It is not an unprimeable number, because it can be changed into a prime (21105971) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8788 + ... + 10928.

It is an arithmetic number, because the mean of its divisors is an integer number (1388016).

Almost surely, 2^21105978 is an apocalyptic number.

21105978 is an abundant number, since it is smaller than the sum of its proper divisors (23310534).

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

21105978 is a wasteful number, since it uses less digits than its factorization.

21105978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2230.

The product of its (nonzero) digits is 5040, while the sum is 33.

The square root of 21105978 is about 4594.1242908742. The cubic root of 21105978 is about 276.3557427064.

The spelling of 21105978 in words is "twenty-one million, one hundred five thousand, nine hundred seventy-eight".