21799561 has 27 divisors (see below), whose sum is σ = 27454791. Its totient is φ = 17256624.

The previous prime is 21799553. The next prime is 21799567. The reversal of 21799561 is 16599712.

The square root of 21799561 is 4669.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 11431161 + 10368400 = 3381^2 + 3220^2 .

It is not a de Polignac number, because 21799561 - 2³ = 21799553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21799567) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 751695 + ... + 751723.

Almost surely, 2^21799561 is an apocalyptic number.

21799561 is the 4669-th square number.

21799561 is the 2335-th centered octagonal number.

It is an amenable number.

21799561 is a deficient number, since it is larger than the sum of its proper divisors (5655230).

21799561 is an equidigital number, since it uses as much as digits as its factorization.

21799561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 118 (or 59 counting only the distinct ones).

The product of its digits is 34020, while the sum is 40.

The cubic root of 21799561 is about 279.3503689496.

The spelling of 21799561 in words is "twenty-one million, seven hundred ninety-nine thousand, five hundred sixty-one".