21128975 has 12 divisors (see below), whose sum is σ = 29943024. Its totient is φ = 14488320.

The previous prime is 21128971. The next prime is 21129037. The reversal of 21128975 is 57982112.

It is not a de Polignac number, because 21128975 - 2² = 21128971 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21128971) 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, 60194 + ... + 60543.

It is an arithmetic number, because the mean of its divisors is an integer number (2495252).

Almost surely, 2^21128975 is an apocalyptic number.

21128975 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21128975 is a deficient number, since it is larger than the sum of its proper divisors (8814049).

21128975 is a wasteful number, since it uses less digits than its factorization.

21128975 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120754 (or 120749 counting only the distinct ones).

The product of its digits is 10080, while the sum is 35.

The square root of 21128975 is about 4596.6264803658. The cubic root of 21128975 is about 276.4560783578.

The spelling of 21128975 in words is "twenty-one million, one hundred twenty-eight thousand, nine hundred seventy-five".