21385717 has 2 divisors, whose sum is σ = 21385718. Its totient is φ = 21385716.

The previous prime is 21385709. The next prime is 21385733. The reversal of 21385717 is 71758312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 96721 = 4614^2 + 311^2 .

It is a cyclic number.

It is not a de Polignac number, because 21385717 - 2³ = 21385709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21385757) 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, 10692858 + 10692859.

It is an arithmetic number, because the mean of its divisors is an integer number (10692859).

Almost surely, 2^21385717 is an apocalyptic number.

It is an amenable number.

21385717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21385717 is an equidigital number, since it uses as much as digits as its factorization.

21385717 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11760, while the sum is 34.

The square root of 21385717 is about 4624.4693749662. The cubic root of 21385717 is about 277.5713292276.

The spelling of 21385717 in words is "twenty-one million, three hundred eighty-five thousand, seven hundred seventeen".