21243531 has 8 divisors (see below), whose sum is σ = 28362960. Its totient is φ = 14143232.

The previous prime is 21243527. The next prime is 21243533. The reversal of 21243531 is 13534212.

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 21243531 - 2² = 21243527 is a prime.

It is a super-2 number, since 2×21243531² = 902575218695922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21243498 and 21243507.

It is not an unprimeable number, because it can be changed into a prime (21243533) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1950 + ... + 6803.

It is an arithmetic number, because the mean of its divisors is an integer number (3545370).

Almost surely, 2^21243531 is an apocalyptic number.

21243531 is a deficient number, since it is larger than the sum of its proper divisors (7119429).

21243531 is an equidigital number, since it uses as much as digits as its factorization.

21243531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9565.

The product of its digits is 720, while the sum is 21.

The square root of 21243531 is about 4609.0705136719. The cubic root of 21243531 is about 276.9548032798.

Adding to 21243531 its reverse (13534212), we get a palindrome (34777743).

The spelling of 21243531 in words is "twenty-one million, two hundred forty-three thousand, five hundred thirty-one".