21245731 has 8 divisors (see below), whose sum is σ = 22921920. Its totient is φ = 19575552.

The previous prime is 21245729. The next prime is 21245737. The reversal of 21245731 is 13754212.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21245731 - 2¹ = 21245729 is a prime.

It is a super-2 number, since 2×21245731² = 902762171448722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21245696 and 21245705.

It is not an unprimeable number, because it can be changed into a prime (21245737) 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 7 ways as a sum of consecutive naturals, for example, 8211 + ... + 10483.

It is an arithmetic number, because the mean of its divisors is an integer number (2865240).

Almost surely, 2^21245731 is an apocalyptic number.

21245731 is a deficient number, since it is larger than the sum of its proper divisors (1676189).

21245731 is a wasteful number, since it uses less digits than its factorization.

21245731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3005.

The product of its digits is 1680, while the sum is 25.

The square root of 21245731 is about 4609.3091673265. The cubic root of 21245731 is about 276.9643635162.

Adding to 21245731 its reverse (13754212), we get a palindrome (34999943).

The spelling of 21245731 in words is "twenty-one million, two hundred forty-five thousand, seven hundred thirty-one".