21210978 has 8 divisors (see below), whose sum is σ = 42421968. Its totient is φ = 7070324.

The previous prime is 21210961. The next prime is 21210979. The reversal of 21210978 is 87901212.

It is a sphenic number, since it is the product of 3 distinct primes.

21210978 is an admirable number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21210979) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1767576 + ... + 1767587.

It is an arithmetic number, because the mean of its divisors is an integer number (5302746).

Almost surely, 2^21210978 is an apocalyptic number.

21210978 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21210978 is a wasteful number, since it uses less digits than its factorization.

21210978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3535168.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 21210978 is about 4605.5377536179. The cubic root of 21210978 is about 276.8132649957.

The spelling of 21210978 in words is "twenty-one million, two hundred ten thousand, nine hundred seventy-eight".