21406990 has 16 divisors (see below), whose sum is σ = 42035760. Its totient is φ = 7784320.

The previous prime is 21406967. The next prime is 21406999. The reversal of 21406990 is 9960412.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21406999) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 97195 + ... + 97414.

It is an arithmetic number, because the mean of its divisors is an integer number (2627235).

Almost surely, 2^21406990 is an apocalyptic number.

21406990 is a deficient number, since it is larger than the sum of its proper divisors (20628770).

21406990 is a wasteful number, since it uses less digits than its factorization.

21406990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 194627.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 21406990 is about 4626.7688509369. The cubic root of 21406990 is about 277.6633348418.

The spelling of 21406990 in words is "twenty-one million, four hundred six thousand, nine hundred ninety".