21687919 has 12 divisors (see below), whose sum is σ = 24878448. Its totient is φ = 18856640.

The previous prime is 21687881. The next prime is 21687923. The reversal of 21687919 is 91978612.

It is a de Polignac number, because none of the positive numbers 2^k-21687919 is a prime.

It is a super-2 number, since 2×21687919² = 940731661101122, 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 (21687959) 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, 1114 + ... + 6679.

It is an arithmetic number, because the mean of its divisors is an integer number (2073204).

Almost surely, 2^21687919 is an apocalyptic number.

21687919 is a deficient number, since it is larger than the sum of its proper divisors (3190529).

21687919 is a wasteful number, since it uses less digits than its factorization.

21687919 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7838 (or 7827 counting only the distinct ones).

The product of its digits is 54432, while the sum is 43.

The square root of 21687919 is about 4657.0289885291. The cubic root of 21687919 is about 278.8726739237.

The spelling of 21687919 in words is "twenty-one million, six hundred eighty-seven thousand, nine hundred nineteen".