21681869 has 12 divisors (see below), whose sum is σ = 25089120. Its totient is φ = 18671400.

The previous prime is 21681839. The next prime is 21681871. The reversal of 21681869 is 96818612.

It is a de Polignac number, because none of the positive numbers 2^k-21681869 is a prime.

It is a super-2 number, since 2×21681869² = 940206886666322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681839) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2417 + ... + 7014.

It is an arithmetic number, because the mean of its divisors is an integer number (2090760).

Almost surely, 2^21681869 is an apocalyptic number.

It is an amenable number.

21681869 is a deficient number, since it is larger than the sum of its proper divisors (3407251).

21681869 is a wasteful number, since it uses less digits than its factorization.

21681869 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9472 (or 9461 counting only the distinct ones).

The product of its digits is 41472, while the sum is 41.

The square root of 21681869 is about 4656.3793874640. The cubic root of 21681869 is about 278.8467403369.

The spelling of 21681869 in words is "twenty-one million, six hundred eighty-one thousand, eight hundred sixty-nine".