21206731 has 16 divisors (see below), whose sum is σ = 26599104. Its totient is φ = 16458624.

The previous prime is 21206699. The next prime is 21206747. The reversal of 21206731 is 13760212.

It is not a de Polignac number, because 21206731 - 2⁵ = 21206699 is a prime.

It is a super-2 number, since 2×21206731² = 899450879412722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21206791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2625 + ... + 7021.

It is an arithmetic number, because the mean of its divisors is an integer number (1662444).

Almost surely, 2^21206731 is an apocalyptic number.

21206731 is a deficient number, since it is larger than the sum of its proper divisors (5392373).

21206731 is a wasteful number, since it uses less digits than its factorization.

21206731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4470.

The product of its (nonzero) digits is 504, while the sum is 22.

The square root of 21206731 is about 4605.0766551709. The cubic root of 21206731 is about 276.7947886450.

Adding to 21206731 its reverse (13760212), we get a palindrome (34966943).

The spelling of 21206731 in words is "twenty-one million, two hundred six thousand, seven hundred thirty-one".