21563539 has 2 divisors, whose sum is σ = 21563540. Its totient is φ = 21563538.

The previous prime is 21563519. The next prime is 21563557. The reversal of 21563539 is 93536512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21563539 - 2²¹ = 19466387 is a prime.

It is not a weakly prime, because it can be changed into another prime (21563519) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10781769 + 10781770.

It is an arithmetic number, because the mean of its divisors is an integer number (10781770).

Almost surely, 2^21563539 is an apocalyptic number.

21563539 is a deficient number, since it is larger than the sum of its proper divisors (1).

21563539 is an equidigital number, since it uses as much as digits as its factorization.

21563539 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 24300, while the sum is 34.

The square root of 21563539 is about 4643.6557796633. The cubic root of 21563539 is about 278.3385408646.

The spelling of 21563539 in words is "twenty-one million, five hundred sixty-three thousand, five hundred thirty-nine".