21287369 has 4 divisors (see below), whose sum is σ = 21450000. Its totient is φ = 21124740.

The previous prime is 21287347. The next prime is 21287389. The reversal of 21287369 is 96378212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21287369 - 2²⁴ = 4510153 is a prime.

It is a super-2 number, since 2×21287369² = 906304157884322, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21287309) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 81119 + ... + 81380.

It is an arithmetic number, because the mean of its divisors is an integer number (5362500).

Almost surely, 2^21287369 is an apocalyptic number.

It is an amenable number.

21287369 is a deficient number, since it is larger than the sum of its proper divisors (162631).

21287369 is a wasteful number, since it uses less digits than its factorization.

21287369 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 162630.

The product of its digits is 36288, while the sum is 38.

The square root of 21287369 is about 4613.8236854045. The cubic root of 21287369 is about 277.1451797097.

The spelling of 21287369 in words is "twenty-one million, two hundred eighty-seven thousand, three hundred sixty-nine".