21539906 has 8 divisors (see below), whose sum is σ = 32430780. Its totient is φ = 10729648.

The previous prime is 21539899. The next prime is 21539933. The reversal of 21539906 is 60993512.

It can be written as a sum of positive squares in 2 ways, for example, as 21242881 + 297025 = 4609^2 + 545^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19481 + ... + 20556.

Almost surely, 2^21539906 is an apocalyptic number.

21539906 is a deficient number, since it is larger than the sum of its proper divisors (10890874).

21539906 is a wasteful number, since it uses less digits than its factorization.

21539906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40308.

The product of its (nonzero) digits is 14580, while the sum is 35.

The square root of 21539906 is about 4641.1104274731. The cubic root of 21539906 is about 278.2368200959.

The spelling of 21539906 in words is "twenty-one million, five hundred thirty-nine thousand, nine hundred six".