21128539 has 2 divisors, whose sum is σ = 21128540. Its totient is φ = 21128538.

The previous prime is 21128507. The next prime is 21128543. The reversal of 21128539 is 93582112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21128539 - 2⁵ = 21128507 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21128539.

It is not a weakly prime, because it can be changed into another prime (21108539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564269 + 10564270.

It is an arithmetic number, because the mean of its divisors is an integer number (10564270).

Almost surely, 2^21128539 is an apocalyptic number.

21128539 is a deficient number, since it is larger than the sum of its proper divisors (1).

21128539 is an equidigital number, since it uses as much as digits as its factorization.

21128539 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 31.

The square root of 21128539 is about 4596.5790540357. The cubic root of 21128539 is about 276.4541767719.

The spelling of 21128539 in words is "twenty-one million, one hundred twenty-eight thousand, five hundred thirty-nine".