21539713 has 4 divisors (see below), whose sum is σ = 23196628. Its totient is φ = 19882800.

The previous prime is 21539701. The next prime is 21539717. The reversal of 21539713 is 31793512.

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 1181569 + 20358144 = 1087^2 + 4512^2 .

It is a cyclic number.

It is not a de Polignac number, because 21539713 - 2⁵ = 21539681 is a prime.

It is a super-2 number, since 2×21539713² = 927918472244738, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21539717) 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, 828438 + ... + 828463.

It is an arithmetic number, because the mean of its divisors is an integer number (5799157).

Almost surely, 2^21539713 is an apocalyptic number.

It is an amenable number.

21539713 is a deficient number, since it is larger than the sum of its proper divisors (1656915).

21539713 is a wasteful number, since it uses less digits than its factorization.

21539713 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1656914.

The product of its digits is 5670, while the sum is 31.

The square root of 21539713 is about 4641.0896349887. The cubic root of 21539713 is about 278.2359890822.

It can be divided in two parts, 215397 and 13, that multiplied together give a triangular number (2800161 = T₂₃₆₆).

The spelling of 21539713 in words is "twenty-one million, five hundred thirty-nine thousand, seven hundred thirteen".