21720563 has 2 divisors, whose sum is σ = 21720564. Its totient is φ = 21720562.

The previous prime is 21720511. The next prime is 21720571. The reversal of 21720563 is 36502712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21720563 - 2⁶ = 21720499 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21720583) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860281 + 10860282.

It is an arithmetic number, because the mean of its divisors is an integer number (10860282).

Almost surely, 2^21720563 is an apocalyptic number.

21720563 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720563 is an equidigital number, since it uses as much as digits as its factorization.

21720563 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2520, while the sum is 26.

The square root of 21720563 is about 4660.5324803074. The cubic root of 21720563 is about 279.0125206887.

The spelling of 21720563 in words is "twenty-one million, seven hundred twenty thousand, five hundred sixty-three".