21055745 has 4 divisors (see below), whose sum is σ = 25266900. Its totient is φ = 16844592.

The previous prime is 21055739. The next prime is 21055759. The reversal of 21055745 is 54755012.

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 16056049 + 4999696 = 4007^2 + 2236^2 .

It is a cyclic number.

It is not a de Polignac number, because 21055745 - 2¹⁶ = 20990209 is a prime.

It is a super-3 number, since 3×21055745³ (a number of 23 digits) contains 333 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2105570 + ... + 2105579.

It is an arithmetic number, because the mean of its divisors is an integer number (6316725).

Almost surely, 2^21055745 is an apocalyptic number.

It is an amenable number.

21055745 is a deficient number, since it is larger than the sum of its proper divisors (4211155).

21055745 is an equidigital number, since it uses as much as digits as its factorization.

21055745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4211154.

The product of its (nonzero) digits is 7000, while the sum is 29.

The square root of 21055745 is about 4588.6539420619. The cubic root of 21055745 is about 276.1363229449.

It can be divided in two parts, 210 and 55745, that added together give a palindrome (55955).

The spelling of 21055745 in words is "twenty-one million, fifty-five thousand, seven hundred forty-five".