21235561 has 4 divisors (see below), whose sum is σ = 21254724. Its totient is φ = 21216400.

The previous prime is 21235549. The next prime is 21235573. The reversal of 21235561 is 16553212.

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

It is an interprime number because it is at equal distance from previous prime (21235549) and next prime (21235573).

It can be written as a sum of positive squares in 2 ways, for example, as 20529961 + 705600 = 4531^2 + 840^2 .

It is a cyclic number.

It is not a de Polignac number, because 21235561 - 2¹⁵ = 21202793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21235061) 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, 7810 + ... + 10171.

It is an arithmetic number, because the mean of its divisors is an integer number (5313681).

Almost surely, 2^21235561 is an apocalyptic number.

It is an amenable number.

21235561 is a deficient number, since it is larger than the sum of its proper divisors (19163).

21235561 is a wasteful number, since it uses less digits than its factorization.

21235561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19162.

The product of its digits is 1800, while the sum is 25.

The square root of 21235561 is about 4608.2058330765. The cubic root of 21235561 is about 276.9201636228.

Adding to 21235561 its reverse (16553212), we get a palindrome (37788773).

The spelling of 21235561 in words is "twenty-one million, two hundred thirty-five thousand, five hundred sixty-one".