21661231 has 4 divisors (see below), whose sum is σ = 22408200. Its totient is φ = 20914264.

The previous prime is 21661223. The next prime is 21661253. The reversal of 21661231 is 13216612.

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 21661231 - 2³ = 21661223 is a prime.

It is a super-2 number, since 2×21661231² = 938417856870722, 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 (21661271) 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, 373441 + ... + 373498.

It is an arithmetic number, because the mean of its divisors is an integer number (5602050).

Almost surely, 2^21661231 is an apocalyptic number.

21661231 is a deficient number, since it is larger than the sum of its proper divisors (746969).

21661231 is an equidigital number, since it uses as much as digits as its factorization.

21661231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 746968.

The product of its digits is 432, while the sum is 22.

The square root of 21661231 is about 4654.1627603684. The cubic root of 21661231 is about 278.7582383430.

Adding to 21661231 its reverse (13216612), we get a palindrome (34877843).

The spelling of 21661231 in words is "twenty-one million, six hundred sixty-one thousand, two hundred thirty-one".