21660187 has 4 divisors (see below), whose sum is σ = 22407120. Its totient is φ = 20913256.

The previous prime is 21660173. The next prime is 21660211. The reversal of 21660187 is 78106612.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21660187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21660127) 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, 373423 + ... + 373480.

It is an arithmetic number, because the mean of its divisors is an integer number (5601780).

Almost surely, 2^21660187 is an apocalyptic number.

21660187 is a deficient number, since it is larger than the sum of its proper divisors (746933).

21660187 is an equidigital number, since it uses as much as digits as its factorization.

21660187 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 746932.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21660187 is about 4654.0506013579. The cubic root of 21660187 is about 278.7537598613.

Adding to 21660187 its reverse (78106612), we get a palindrome (99766799).

The spelling of 21660187 in words is "twenty-one million, six hundred sixty thousand, one hundred eighty-seven".