21711645 has 20 divisors (see below), whose sum is σ = 38920860. Its totient is φ = 11579328.

The previous prime is 21711619. The next prime is 21711709. The reversal of 21711645 is 54611712.

It is a happy number.

21711645 is a `hidden beast` number, since 2 + 1 + 7 + 11 + 645 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 2893401 + 18818244 = 1701^2 + 4338^2 .

It is not a de Polignac number, because 21711645 - 2⁶ = 21711581 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

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 19 ways as a sum of consecutive naturals, for example, 26400 + ... + 27209.

It is an arithmetic number, because the mean of its divisors is an integer number (1946043).

Almost surely, 2^21711645 is an apocalyptic number.

It is an amenable number.

21711645 is a deficient number, since it is larger than the sum of its proper divisors (17209215).

21711645 is an equidigital number, since it uses as much as digits as its factorization.

21711645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53626 (or 53617 counting only the distinct ones).

The product of its digits is 1680, while the sum is 27.

The square root of 21711645 is about 4659.5756244534. The cubic root of 21711645 is about 278.9743299310.

The spelling of 21711645 in words is "twenty-one million, seven hundred eleven thousand, six hundred forty-five".