21687371 has 4 divisors (see below), whose sum is σ = 21898032. Its totient is φ = 21476712.

The previous prime is 21687361. The next prime is 21687373. The reversal of 21687371 is 17378612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21687371 - 2⁶ = 21687307 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21687373) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 105176 + ... + 105381.

It is an arithmetic number, because the mean of its divisors is an integer number (5474508).

Almost surely, 2^21687371 is an apocalyptic number.

21687371 is a deficient number, since it is larger than the sum of its proper divisors (210661).

21687371 is a wasteful number, since it uses less digits than its factorization.

21687371 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 210660.

The product of its digits is 14112, while the sum is 35.

The square root of 21687371 is about 4656.9701523630. The cubic root of 21687371 is about 278.8703250966.

The spelling of 21687371 in words is "twenty-one million, six hundred eighty-seven thousand, three hundred seventy-one".