21809719 has 2 divisors, whose sum is σ = 21809720. Its totient is φ = 21809718.

The previous prime is 21809693. The next prime is 21809737. The reversal of 21809719 is 91790812.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21809719 is a prime.

It is a super-2 number, since 2×21809719² = 951327685717922, which contains 22 as substring.

It is equal to p_1377946 and since 21809719 and 1377946 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21809779) 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, 10904859 + 10904860.

It is an arithmetic number, because the mean of its divisors is an integer number (10904860).

Almost surely, 2^21809719 is an apocalyptic number.

21809719 is a deficient number, since it is larger than the sum of its proper divisors (1).

21809719 is an equidigital number, since it uses as much as digits as its factorization.

21809719 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 21809719 is about 4670.0876865429. The cubic root of 21809719 is about 279.3937520924.

The spelling of 21809719 in words is "twenty-one million, eight hundred nine thousand, seven hundred nineteen".