21085745 has 16 divisors (see below), whose sum is σ = 26142480. Its totient is φ = 16314624.

The previous prime is 21085739. The next prime is 21085747. The reversal of 21085745 is 54758012.

It can be written as a sum of positive squares in 8 ways, for example, as 1760929 + 19324816 = 1327^2 + 4396^2 .

It is a cyclic number.

It is not a de Polignac number, because 21085745 - 2¹⁴ = 21069361 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21085747) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 54011 + ... + 54399.

It is an arithmetic number, because the mean of its divisors is an integer number (1633905).

Almost surely, 2^21085745 is an apocalyptic number.

It is an amenable number.

21085745 is a deficient number, since it is larger than the sum of its proper divisors (5056735).

21085745 is a wasteful number, since it uses less digits than its factorization.

21085745 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 724.

The product of its (nonzero) digits is 11200, while the sum is 32.

The square root of 21085745 is about 4591.9217110051. The cubic root of 21085745 is about 276.2674060680.

The spelling of 21085745 in words is "twenty-one million, eighty-five thousand, seven hundred forty-five".