21172731 has 8 divisors (see below), whose sum is σ = 28510224. Its totient is φ = 13975200.

The previous prime is 21172717. The next prime is 21172733. The reversal of 21172731 is 13727112.

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

It is not a de Polignac number, because 21172731 - 2¹⁷ = 21041659 is a prime.

It is a super-2 number, since 2×21172731² = 896569075996722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21172733) 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 7 ways as a sum of consecutive naturals, for example, 34636 + ... + 35241.

It is an arithmetic number, because the mean of its divisors is an integer number (3563778).

Almost surely, 2^21172731 is an apocalyptic number.

21172731 is a deficient number, since it is larger than the sum of its proper divisors (7337493).

21172731 is a wasteful number, since it uses less digits than its factorization.

21172731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69981.

The product of its digits is 588, while the sum is 24.

The square root of 21172731 is about 4601.3835962675. The cubic root of 21172731 is about 276.6467844295.

Adding to 21172731 its reverse (13727112), we get a palindrome (34899843).

The spelling of 21172731 in words is "twenty-one million, one hundred seventy-two thousand, seven hundred thirty-one".