21005559 has 6 divisors (see below), whose sum is σ = 30341376. Its totient is φ = 14003700.

The previous prime is 21005539. The next prime is 21005561. The reversal of 21005559 is 95550012.

21005559 is a `hidden beast` number, since 2 + 100 + 5 + 559 = 666.

It is not a de Polignac number, because 21005559 - 2¹⁹ = 20481271 is a prime.

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 pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1166967 + ... + 1166984.

It is an arithmetic number, because the mean of its divisors is an integer number (5056896).

Almost surely, 2^21005559 is an apocalyptic number.

21005559 is a deficient number, since it is larger than the sum of its proper divisors (9335817).

21005559 is a wasteful number, since it uses less digits than its factorization.

21005559 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2333957 (or 2333954 counting only the distinct ones).

The product of its (nonzero) digits is 2250, while the sum is 27.

The square root of 21005559 is about 4583.1821914473. The cubic root of 21005559 is about 275.9167597118.

The spelling of 21005559 in words is "twenty-one million, five thousand, five hundred fifty-nine".