21242731 has 16 divisors (see below), whose sum is σ = 23215104. Its totient is φ = 19381824.

The previous prime is 21242729. The next prime is 21242747. The reversal of 21242731 is 13724212.

It is not a de Polignac number, because 21242731 - 2¹ = 21242729 is a prime.

It is a super-2 number, since 2×21242731² = 902507240676722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21242131) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 46255 + ... + 46711.

It is an arithmetic number, because the mean of its divisors is an integer number (1450944).

Almost surely, 2^21242731 is an apocalyptic number.

21242731 is a deficient number, since it is larger than the sum of its proper divisors (1972373).

21242731 is a wasteful number, since it uses less digits than its factorization.

21242731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 570.

The product of its digits is 672, while the sum is 22.

The square root of 21242731 is about 4608.9837274610. The cubic root of 21242731 is about 276.9513266666.

Adding to 21242731 its reverse (13724212), we get a palindrome (34966943).

The spelling of 21242731 in words is "twenty-one million, two hundred forty-two thousand, seven hundred thirty-one".