21105639 has 12 divisors (see below), whose sum is σ = 30562272. Its totient is φ = 14035200.

The previous prime is 21105587. The next prime is 21105641. The reversal of 21105639 is 93650112.

21105639 is a `hidden beast` number, since 21 + 1 + 0 + 5 + 639 = 666.

It is not a de Polignac number, because 21105639 - 2¹⁷ = 20974567 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105659) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1159 + ... + 6599.

It is an arithmetic number, because the mean of its divisors is an integer number (2546856).

Almost surely, 2^21105639 is an apocalyptic number.

21105639 is a deficient number, since it is larger than the sum of its proper divisors (9456633).

21105639 is a wasteful number, since it uses less digits than its factorization.

21105639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5878 (or 5875 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 27.

The square root of 21105639 is about 4594.0873957730. The cubic root of 21105639 is about 276.3542631082.

The spelling of 21105639 in words is "twenty-one million, one hundred five thousand, six hundred thirty-nine".