21520231 has 4 divisors (see below), whose sum is σ = 22214464. Its totient is φ = 20826000.

The previous prime is 21520229. The next prime is 21520241. The reversal of 21520231 is 13202512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21520231 - 2¹ = 21520229 is a prime.

It is a super-2 number, since 2×21520231² = 926240684586722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520241) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 347070 + ... + 347131.

It is an arithmetic number, because the mean of its divisors is an integer number (5553616).

Almost surely, 2^21520231 is an apocalyptic number.

21520231 is a deficient number, since it is larger than the sum of its proper divisors (694233).

21520231 is an equidigital number, since it uses as much as digits as its factorization.

21520231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 694232.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21520231 is about 4638.9902996234. The cubic root of 21520231 is about 278.1520785149.

Adding to 21520231 its reverse (13202512), we get a palindrome (34722743).

The spelling of 21520231 in words is "twenty-one million, five hundred twenty thousand, two hundred thirty-one".