21785245 has 16 divisors (see below), whose sum is σ = 27841968. Its totient is φ = 16307200.

The previous prime is 21785243. The next prime is 21785249. The reversal of 21785245 is 54258712.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 13689 + 21771556 = 117^2 + 4666^2 .

It is not a de Polignac number, because 21785245 - 2¹ = 21785243 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21785245.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21785243) 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, 16095 + ... + 17395.

It is an arithmetic number, because the mean of its divisors is an integer number (1740123).

Almost surely, 2^21785245 is an apocalyptic number.

It is an amenable number.

21785245 is a deficient number, since it is larger than the sum of its proper divisors (6056723).

21785245 is a wasteful number, since it uses less digits than its factorization.

21785245 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1520.

The product of its digits is 22400, while the sum is 34.

The square root of 21785245 is about 4667.4666576206. The cubic root of 21785245 is about 279.2892047876.

The spelling of 21785245 in words is "twenty-one million, seven hundred eighty-five thousand, two hundred forty-five".