21231561 has 8 divisors (see below), whose sum is σ = 30486400. Its totient is φ = 13065552.

The previous prime is 21231557. The next prime is 21231577. The reversal of 21231561 is 16513212.

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

It is not a de Polignac number, because 21231561 - 2² = 21231557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21231761) 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, 272161 + ... + 272238.

It is an arithmetic number, because the mean of its divisors is an integer number (3810800).

Almost surely, 2^21231561 is an apocalyptic number.

It is an amenable number.

21231561 is a deficient number, since it is larger than the sum of its proper divisors (9254839).

21231561 is a wasteful number, since it uses less digits than its factorization.

21231561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 544415.

The product of its digits is 360, while the sum is 21.

The square root of 21231561 is about 4607.7718042455. The cubic root of 21231561 is about 276.9027753339.

Adding to 21231561 its reverse (16513212), we get a palindrome (37744773).

The spelling of 21231561 in words is "twenty-one million, two hundred thirty-one thousand, five hundred sixty-one".