21328551 has 6 divisors (see below), whose sum is σ = 30807920. Its totient is φ = 14219028.

The previous prime is 21328537. The next prime is 21328561. The reversal of 21328551 is 15582312.

It is a happy number.

It is not a de Polignac number, because 21328551 - 2⁷ = 21328423 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21328501) 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 5 ways as a sum of consecutive naturals, for example, 1184911 + ... + 1184928.

Almost surely, 2^21328551 is an apocalyptic number.

21328551 is a deficient number, since it is larger than the sum of its proper divisors (9479369).

21328551 is a wasteful number, since it uses less digits than its factorization.

21328551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2369845 (or 2369842 counting only the distinct ones).

The product of its digits is 2400, while the sum is 27.

The square root of 21328551 is about 4618.2844217306. The cubic root of 21328551 is about 277.3237839119.

The spelling of 21328551 in words is "twenty-one million, three hundred twenty-eight thousand, five hundred fifty-one".