21005549 has 4 divisors (see below), whose sum is σ = 21016764. Its totient is φ = 20994336.

The previous prime is 21005539. The next prime is 21005561. The reversal of 21005549 is 94550012.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 16933225 + 4072324 = 4115^2 + 2018^2 .

It is a cyclic number.

It is not a de Polignac number, because 21005549 - 2⁸ = 21005293 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 (21005539) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2042 + ... + 6795.

It is an arithmetic number, because the mean of its divisors is an integer number (5254191).

Almost surely, 2^21005549 is an apocalyptic number.

It is an amenable number.

21005549 is a deficient number, since it is larger than the sum of its proper divisors (11215).

21005549 is an equidigital number, since it uses as much as digits as its factorization.

21005549 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11214.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21005549 is about 4583.1811005021. The cubic root of 21005549 is about 275.9167159270.

The spelling of 21005549 in words is "twenty-one million, five thousand, five hundred forty-nine".