21393990 has 128 divisors (see below), whose sum is σ = 62208000. Its totient is φ = 5211648.

The previous prime is 21393989. The next prime is 21394063. The reversal of 21393990 is 9939312.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 270771 + ... + 270849.

It is an arithmetic number, because the mean of its divisors is an integer number (486000).

Almost surely, 2^21393990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21393990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31104000).

21393990 is an abundant number, since it is smaller than the sum of its proper divisors (40814010).

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

21393990 is a wasteful number, since it uses less digits than its factorization.

21393990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171 (or 165 counting only the distinct ones).

The product of its (nonzero) digits is 13122, while the sum is 36.

The square root of 21393990 is about 4625.3637694780. The cubic root of 21393990 is about 277.6071171565.

The spelling of 21393990 in words is "twenty-one million, three hundred ninety-three thousand, nine hundred ninety".