21704187 has 4 divisors (see below), whose sum is σ = 28938920. Its totient is φ = 14469456.

The previous prime is 21704171. The next prime is 21704191. The reversal of 21704187 is 78140712.

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

It is not a de Polignac number, because 21704187 - 2⁴ = 21704171 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21704107) 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, 3617362 + ... + 3617367.

It is an arithmetic number, because the mean of its divisors is an integer number (7234730).

Almost surely, 2^21704187 is an apocalyptic number.

21704187 is a deficient number, since it is larger than the sum of its proper divisors (7234733).

21704187 is an equidigital number, since it uses as much as digits as its factorization.

21704187 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7234732.

The product of its (nonzero) digits is 3136, while the sum is 30.

The square root of 21704187 is about 4658.7752682438. The cubic root of 21704187 is about 278.9423834981.

Adding to 21704187 its reverse (78140712), we get a palindrome (99844899).

The spelling of 21704187 in words is "twenty-one million, seven hundred four thousand, one hundred eighty-seven".