21005539 has 2 divisors, whose sum is σ = 21005540. Its totient is φ = 21005538.

The previous prime is 21005503. The next prime is 21005561. The reversal of 21005539 is 93550012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21005539 - 2¹¹ = 21003491 is a prime.

It is not a weakly prime, because it can be changed into another prime (21005339) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10502769 + 10502770.

It is an arithmetic number, because the mean of its divisors is an integer number (10502770).

Almost surely, 2^21005539 is an apocalyptic number.

21005539 is a deficient number, since it is larger than the sum of its proper divisors (1).

21005539 is an equidigital number, since it uses as much as digits as its factorization.

21005539 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1350, while the sum is 25.

The square root of 21005539 is about 4583.1800095567. The cubic root of 21005539 is about 275.9166721423.

The spelling of 21005539 in words is "twenty-one million, five thousand, five hundred thirty-nine".