21775561 has 4 divisors (see below), whose sum is σ = 21789124. Its totient is φ = 21762000.

The previous prime is 21775531. The next prime is 21775571. The reversal of 21775561 is 16557712.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 6125625 + 15649936 = 2475^2 + 3956^2 .

It is a cyclic number.

It is not a de Polignac number, because 21775561 - 2⁹ = 21775049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21775531) 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, 3990 + ... + 7711.

It is an arithmetic number, because the mean of its divisors is an integer number (5447281).

Almost surely, 2^21775561 is an apocalyptic number.

It is an amenable number.

21775561 is a deficient number, since it is larger than the sum of its proper divisors (13563).

21775561 is a wasteful number, since it uses less digits than its factorization.

21775561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13562.

The product of its digits is 14700, while the sum is 34.

The square root of 21775561 is about 4666.4291487175. The cubic root of 21775561 is about 279.2478153439.

The spelling of 21775561 in words is "twenty-one million, seven hundred seventy-five thousand, five hundred sixty-one".