21042685 has 16 divisors (see below), whose sum is σ = 26862192. Its totient is φ = 15769600.

The previous prime is 21042649. The next prime is 21042689. The reversal of 21042685 is 58624012.

It can be written as a sum of positive squares in 8 ways, for example, as 2116 + 21040569 = 46^2 + 4587^2 .

It is not a de Polignac number, because 21042685 - 2¹⁷ = 20911613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21042689) 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 in 15 ways as a sum of consecutive naturals, for example, 23445 + ... + 24325.

It is an arithmetic number, because the mean of its divisors is an integer number (1678887).

Almost surely, 2^21042685 is an apocalyptic number.

It is an amenable number.

21042685 is a deficient number, since it is larger than the sum of its proper divisors (5819507).

21042685 is a wasteful number, since it uses less digits than its factorization.

21042685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1184.

The product of its (nonzero) digits is 3840, while the sum is 28.

The square root of 21042685 is about 4587.2306460434. The cubic root of 21042685 is about 276.0792191908.

Adding to 21042685 its reverse (58624012), we get a palindrome (79666697).

The spelling of 21042685 in words is "twenty-one million, forty-two thousand, six hundred eighty-five".