21128387 has 8 divisors (see below), whose sum is σ = 24543072. Its totient is φ = 17812800.

The previous prime is 21128381. The next prime is 21128411. The reversal of 21128387 is 78382112.

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

It is a cyclic number.

It is not a de Polignac number, because 21128387 - 2⁸ = 21128131 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21128381) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 24314 + ... + 25167.

It is an arithmetic number, because the mean of its divisors is an integer number (3067884).

Almost surely, 2^21128387 is an apocalyptic number.

21128387 is a deficient number, since it is larger than the sum of its proper divisors (3414685).

21128387 is an equidigital number, since it uses as much as digits as its factorization.

21128387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49549.

The product of its digits is 5376, while the sum is 32.

The square root of 21128387 is about 4596.5625199708. The cubic root of 21128387 is about 276.4535138276.

The spelling of 21128387 in words is "twenty-one million, one hundred twenty-eight thousand, three hundred eighty-seven".