21085717 has 2 divisors, whose sum is σ = 21085718. Its totient is φ = 21085716.

The previous prime is 21085709. The next prime is 21085721. The reversal of 21085717 is 71758012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17648401 + 3437316 = 4201^2 + 1854^2 .

It is a cyclic number.

It is not a de Polignac number, because 21085717 - 2³ = 21085709 is a prime.

It is a super-2 number, since 2×21085717² = 889214922808178, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21085747) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10542858 + 10542859.

It is an arithmetic number, because the mean of its divisors is an integer number (10542859).

Almost surely, 2^21085717 is an apocalyptic number.

It is an amenable number.

21085717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21085717 is an equidigital number, since it uses as much as digits as its factorization.

21085717 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3920, while the sum is 31.

The square root of 21085717 is about 4591.9186621716. The cubic root of 21085717 is about 276.2672837817.

The spelling of 21085717 in words is "twenty-one million, eighty-five thousand, seven hundred seventeen".