21561121 has 16 divisors (see below), whose sum is σ = 23154768. Its totient is φ = 20044800.

The previous prime is 21561107. The next prime is 21561131. The reversal of 21561121 is 12116512.

It can be written as a sum of positive squares in 8 ways, for example, as 5239521 + 16321600 = 2289^2 + 4040^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561121 - 2¹⁹ = 21036833 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21561101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 92421 + ... + 92653.

It is an arithmetic number, because the mean of its divisors is an integer number (1447173).

Almost surely, 2^21561121 is an apocalyptic number.

It is an amenable number.

21561121 is a deficient number, since it is larger than the sum of its proper divisors (1593647).

21561121 is a wasteful number, since it uses less digits than its factorization.

21561121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 372.

The product of its digits is 120, while the sum is 19.

The square root of 21561121 is about 4643.3954171490. The cubic root of 21561121 is about 278.3281367630.

Adding to 21561121 its reverse (12116512), we get a palindrome (33677633).

The spelling of 21561121 in words is "twenty-one million, five hundred sixty-one thousand, one hundred twenty-one".