21171687 has 4 divisors (see below), whose sum is σ = 28228920. Its totient is φ = 14114456.

The previous prime is 21171673. The next prime is 21171701. The reversal of 21171687 is 78617112.

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

It is an interprime number because it is at equal distance from previous prime (21171673) and next prime (21171701).

It is a cyclic number.

It is not a de Polignac number, because 21171687 - 2⁴ = 21171671 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21171617) 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, 3528612 + ... + 3528617.

It is an arithmetic number, because the mean of its divisors is an integer number (7057230).

Almost surely, 2^21171687 is an apocalyptic number.

21171687 is a deficient number, since it is larger than the sum of its proper divisors (7057233).

21171687 is an equidigital number, since it uses as much as digits as its factorization.

21171687 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7057232.

The product of its digits is 4704, while the sum is 33.

The square root of 21171687 is about 4601.2701507301. The cubic root of 21171687 is about 276.6422373230.

Adding to 21171687 its reverse (78617112), we get a palindrome (99788799).

The spelling of 21171687 in words is "twenty-one million, one hundred seventy-one thousand, six hundred eighty-seven".