21218869 has 4 divisors (see below), whose sum is σ = 24250144. Its totient is φ = 18187596.

The previous prime is 21218863. The next prime is 21218887. The reversal of 21218869 is 96881212.

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 not a de Polignac number, because 21218869 - 2³ = 21218861 is a prime.

It is a super-2 number, since 2×21218869² = 900480803278322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218861) 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, 1515627 + ... + 1515640.

It is an arithmetic number, because the mean of its divisors is an integer number (6062536).

Almost surely, 2^21218869 is an apocalyptic number.

It is an amenable number.

21218869 is a deficient number, since it is larger than the sum of its proper divisors (3031275).

21218869 is an equidigital number, since it uses as much as digits as its factorization.

21218869 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3031274.

The product of its digits is 13824, while the sum is 37.

The square root of 21218869 is about 4606.3943600174. The cubic root of 21218869 is about 276.8475878301.

The spelling of 21218869 in words is "twenty-one million, two hundred eighteen thousand, eight hundred sixty-nine".