21566543 has 2 divisors, whose sum is σ = 21566544. Its totient is φ = 21566542.

The previous prime is 21566509. The next prime is 21566551. The reversal of 21566543 is 34566512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21566543 - 2¹⁰ = 21565519 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21566593) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10783271 + 10783272.

It is an arithmetic number, because the mean of its divisors is an integer number (10783272).

Almost surely, 2^21566543 is an apocalyptic number.

21566543 is a deficient number, since it is larger than the sum of its proper divisors (1).

21566543 is an equidigital number, since it uses as much as digits as its factorization.

21566543 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 21600, while the sum is 32.

The square root of 21566543 is about 4643.9792204531. The cubic root of 21566543 is about 278.3514653070.

The spelling of 21566543 in words is "twenty-one million, five hundred sixty-six thousand, five hundred forty-three".