21278390 has 32 divisors (see below), whose sum is σ = 46350144. Its totient is φ = 6865920.

The previous prime is 21278363. The next prime is 21278393. The reversal of 21278390 is 9387212.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21278393) 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, 7751 + ... + 10130.

It is an arithmetic number, because the mean of its divisors is an integer number (1448442).

Almost surely, 2^21278390 is an apocalyptic number.

21278390 is an abundant number, since it is smaller than the sum of its proper divisors (25071754).

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

21278390 is a wasteful number, since it uses less digits than its factorization.

21278390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17912.

The product of its (nonzero) digits is 6048, while the sum is 32.

The square root of 21278390 is about 4612.8505286861. The cubic root of 21278390 is about 277.1062076706.

The spelling of 21278390 in words is "twenty-one million, two hundred seventy-eight thousand, three hundred ninety".