21660559 has 2 divisors, whose sum is σ = 21660560. Its totient is φ = 21660558.

The previous prime is 21660523. The next prime is 21660607. The reversal of 21660559 is 95506612.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21660559 - 2⁹ = 21660047 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21660959) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830279 + 10830280.

It is an arithmetic number, because the mean of its divisors is an integer number (10830280).

Almost surely, 2^21660559 is an apocalyptic number.

21660559 is a deficient number, since it is larger than the sum of its proper divisors (1).

21660559 is an equidigital number, since it uses as much as digits as its factorization.

21660559 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16200, while the sum is 34.

The square root of 21660559 is about 4654.0905663728. The cubic root of 21660559 is about 278.7553556587.

The spelling of 21660559 in words is "twenty-one million, six hundred sixty thousand, five hundred fifty-nine".