21072187 has 2 divisors, whose sum is σ = 21072188. Its totient is φ = 21072186.

The previous prime is 21072169. The next prime is 21072199. The reversal of 21072187 is 78127012.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21072187 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21072137) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10536093 + 10536094.

It is an arithmetic number, because the mean of its divisors is an integer number (10536094).

Almost surely, 2^21072187 is an apocalyptic number.

21072187 is a deficient number, since it is larger than the sum of its proper divisors (1).

21072187 is an equidigital number, since it uses as much as digits as its factorization.

21072187 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1568, while the sum is 28.

The square root of 21072187 is about 4590.4451853824. The cubic root of 21072187 is about 276.2081806437.

Adding to 21072187 its reverse (78127012), we get a palindrome (99199199).

The spelling of 21072187 in words is "twenty-one million, seventy-two thousand, one hundred eighty-seven".