21405806 has 8 divisors (see below), whose sum is σ = 32171904. Its totient is φ = 10681840.

The previous prime is 21405803. The next prime is 21405827. The reversal of 21405806 is 60850412.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405803) 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 3 ways as a sum of consecutive naturals, for example, 9230 + ... + 11313.

It is an arithmetic number, because the mean of its divisors is an integer number (4021488).

Almost surely, 2^21405806 is an apocalyptic number.

21405806 is a deficient number, since it is larger than the sum of its proper divisors (10766098).

21405806 is a wasteful number, since it uses less digits than its factorization.

21405806 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21066.

The product of its (nonzero) digits is 1920, while the sum is 26.

The square root of 21405806 is about 4626.6408981031. The cubic root of 21405806 is about 277.6582156502.

The spelling of 21405806 in words is "twenty-one million, four hundred five thousand, eight hundred six".