21087919 has 2 divisors, whose sum is σ = 21087920. Its totient is φ = 21087918.

The previous prime is 21087917. The next prime is 21087943. The reversal of 21087919 is 91978012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21087919 - 2¹ = 21087917 is a prime.

It is a super-2 number, since 2×21087919² = 889400655501122, which contains 22 as substring.

Together with 21087917, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21087917) 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, 10543959 + 10543960.

It is an arithmetic number, because the mean of its divisors is an integer number (10543960).

Almost surely, 2^21087919 is an apocalyptic number.

21087919 is a deficient number, since it is larger than the sum of its proper divisors (1).

21087919 is an equidigital number, since it uses as much as digits as its factorization.

21087919 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21087919 is about 4592.1584249675. The cubic root of 21087919 is about 276.2769003922.

The spelling of 21087919 in words is "twenty-one million, eighty-seven thousand, nine hundred nineteen".