21309611 has 2 divisors, whose sum is σ = 21309612. Its totient is φ = 21309610.

The previous prime is 21309601. The next prime is 21309623. The reversal of 21309611 is 11690312.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21309611 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21309601) 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, 10654805 + 10654806.

It is an arithmetic number, because the mean of its divisors is an integer number (10654806).

Almost surely, 2^21309611 is an apocalyptic number.

21309611 is a deficient number, since it is larger than the sum of its proper divisors (1).

21309611 is an equidigital number, since it uses as much as digits as its factorization.

21309611 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 324, while the sum is 23.

The square root of 21309611 is about 4616.2334213079. The cubic root of 21309611 is about 277.2416706919.

Adding to 21309611 its reverse (11690312), we get a palindrome (32999923).

The spelling of 21309611 in words is "twenty-one million, three hundred nine thousand, six hundred eleven".