21809069 has 2 divisors, whose sum is σ = 21809070. Its totient is φ = 21809068.

The previous prime is 21809057. The next prime is 21809071. The reversal of 21809069 is 96090812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21808900 + 169 = 4670^2 + 13^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21809069 is a prime.

It is a super-2 number, since 2×21809069² = 951270981293522, which contains 22 as substring.

Together with 21809071, 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 (21809009) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904534 + 10904535.

It is an arithmetic number, because the mean of its divisors is an integer number (10904535).

Almost surely, 2^21809069 is an apocalyptic number.

It is an amenable number.

21809069 is a deficient number, since it is larger than the sum of its proper divisors (1).

21809069 is an equidigital number, since it uses as much as digits as its factorization.

21809069 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7776, while the sum is 35.

The square root of 21809069 is about 4670.0180941834. The cubic root of 21809069 is about 279.3909764531.

The spelling of 21809069 in words is "twenty-one million, eight hundred nine thousand, sixty-nine".