21987569 has 4 divisors (see below), whose sum is σ = 21998580. Its totient is φ = 21976560.

The previous prime is 21987557. The next prime is 21987571. The reversal of 21987569 is 96578912.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 18601969 + 3385600 = 4313^2 + 1840^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21987569 is a prime.

It is a super-2 number, since 2×21987569² = 966906381059522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21987529) 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, 1574 + ... + 6815.

It is an arithmetic number, because the mean of its divisors is an integer number (5499645).

Almost surely, 2^21987569 is an apocalyptic number.

It is an amenable number.

21987569 is a deficient number, since it is larger than the sum of its proper divisors (11011).

21987569 is an equidigital number, since it uses as much as digits as its factorization.

21987569 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11010.

The product of its digits is 272160, while the sum is 47.

The square root of 21987569 is about 4689.0904235257. The cubic root of 21987569 is about 280.1511471359.

The spelling of 21987569 in words is "twenty-one million, nine hundred eighty-seven thousand, five hundred sixty-nine".