21405550 has 24 divisors (see below), whose sum is σ = 42158016. Its totient is φ = 8058240.

The previous prime is 21405523. The next prime is 21405551. The reversal of 21405550 is 5550412.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405551) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11742 + ... + 13441.

It is an arithmetic number, because the mean of its divisors is an integer number (1756584).

Almost surely, 2^21405550 is an apocalyptic number.

21405550 is a deficient number, since it is larger than the sum of its proper divisors (20752466).

21405550 is a wasteful number, since it uses less digits than its factorization.

21405550 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25212 (or 25207 counting only the distinct ones).

The product of its (nonzero) digits is 1000, while the sum is 22.

The square root of 21405550 is about 4626.6132321602. The cubic root of 21405550 is about 277.6571087731.

Adding to 21405550 its reverse (5550412), we get a palindrome (26955962).

The spelling of 21405550 in words is "twenty-one million, four hundred five thousand, five hundred fifty".