21391187 has 2 divisors, whose sum is σ = 21391188. Its totient is φ = 21391186.

The previous prime is 21391133. The next prime is 21391189. The reversal of 21391187 is 78119312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21391187 - 2¹⁰ = 21390163 is a prime.

Together with 21391189, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21391189) 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 as a sum of consecutive naturals, namely, 10695593 + 10695594.

It is an arithmetic number, because the mean of its divisors is an integer number (10695594).

Almost surely, 2^21391187 is an apocalyptic number.

21391187 is a deficient number, since it is larger than the sum of its proper divisors (1).

21391187 is an equidigital number, since it uses as much as digits as its factorization.

21391187 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3024, while the sum is 32.

The square root of 21391187 is about 4625.0607563577. The cubic root of 21391187 is about 277.5949927743.

The spelling of 21391187 in words is "twenty-one million, three hundred ninety-one thousand, one hundred eighty-seven".