21987369 has 14 divisors (see below), whose sum is σ = 32967066. Its totient is φ = 14657760.

The previous prime is 21987331. The next prime is 21987373. The reversal of 21987369 is 96378912.

It can be written as a sum of positive squares in only one way, i.e., 20820969 + 1166400 = 4563^2 + 1080^2 .

It is not a de Polignac number, because 21987369 - 2¹⁵ = 21954601 is a prime.

It is a super-2 number, since 2×21987369² = 966888791084322, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21987169) by changing a digit.

It is a polite number, since it can be written in 13 ways as a sum of consecutive naturals, for example, 14352 + ... + 15809.

Almost surely, 2^21987369 is an apocalyptic number.

It is an amenable number.

21987369 is a deficient number, since it is larger than the sum of its proper divisors (10979697).

21987369 is an frugal number, since it uses more digits than its factorization.

21987369 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30179 (or 30164 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The square root of 21987369 is about 4689.0690973796. The cubic root of 21987369 is about 280.1502977105.

The spelling of 21987369 in words is "twenty-one million, nine hundred eighty-seven thousand, three hundred sixty-nine".