21021685 has 4 divisors (see below), whose sum is σ = 25226028. Its totient is φ = 16817344.

The previous prime is 21021683. The next prime is 21021697. The reversal of 21021685 is 58612012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9284209 + 11737476 = 3047^2 + 3426^2 .

It is a cyclic number.

It is not a de Polignac number, because 21021685 - 2¹ = 21021683 is a prime.

It is a super-2 number, since 2×21021685² = 883822480478450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021683) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2102164 + ... + 2102173.

It is an arithmetic number, because the mean of its divisors is an integer number (6306507).

Almost surely, 2^21021685 is an apocalyptic number.

It is an amenable number.

21021685 is a deficient number, since it is larger than the sum of its proper divisors (4204343).

21021685 is an equidigital number, since it uses as much as digits as its factorization.

21021685 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4204342.

The product of its (nonzero) digits is 960, while the sum is 25.

The square root of 21021685 is about 4584.9411119446. The cubic root of 21021685 is about 275.9873488915.

Adding to 21021685 its reverse (58612012), we get a palindrome (79633697).

The spelling of 21021685 in words is "twenty-one million, twenty-one thousand, six hundred eighty-five".