21666587 has 2 divisors, whose sum is σ = 21666588. Its totient is φ = 21666586.

The previous prime is 21666583. The next prime is 21666611. The reversal of 21666587 is 78566612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21666587 - 2² = 21666583 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21666583) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833293 + 10833294.

It is an arithmetic number, because the mean of its divisors is an integer number (10833294).

Almost surely, 2^21666587 is an apocalyptic number.

21666587 is a deficient number, since it is larger than the sum of its proper divisors (1).

21666587 is an equidigital number, since it uses as much as digits as its factorization.

21666587 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 120960, while the sum is 41.

The square root of 21666587 is about 4654.7381236757. The cubic root of 21666587 is about 278.7812118924.

The spelling of 21666587 in words is "twenty-one million, six hundred sixty-six thousand, five hundred eighty-seven".