21387390 has 16 divisors (see below), whose sum is σ = 51329808. Its totient is φ = 5703296.

The previous prime is 21387389. The next prime is 21387391. The reversal of 21387390 is 9378312.

It is an interprime number because it is at equal distance from previous prime (21387389) and next prime (21387391).

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387391) 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 7 ways as a sum of consecutive naturals, for example, 356427 + ... + 356486.

It is an arithmetic number, because the mean of its divisors is an integer number (3208113).

Almost surely, 2^21387390 is an apocalyptic number.

21387390 is an abundant number, since it is smaller than the sum of its proper divisors (29942418).

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

21387390 is a wasteful number, since it uses less digits than its factorization.

21387390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 712923.

The product of its (nonzero) digits is 9072, while the sum is 33.

The square root of 21387390 is about 4624.6502570465. The cubic root of 21387390 is about 277.5785671538.

The spelling of 21387390 in words is "twenty-one million, three hundred eighty-seven thousand, three hundred ninety".