21968511 has 4 divisors (see below), whose sum is σ = 29291352. Its totient is φ = 14645672.

The previous prime is 21968509. The next prime is 21968543. The reversal of 21968511 is 11586912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21968511 - 2¹ = 21968509 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21968711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3661416 + ... + 3661421.

It is an arithmetic number, because the mean of its divisors is an integer number (7322838).

Almost surely, 2^21968511 is an apocalyptic number.

21968511 is a deficient number, since it is larger than the sum of its proper divisors (7322841).

21968511 is an equidigital number, since it uses as much as digits as its factorization.

21968511 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7322840.

The product of its digits is 4320, while the sum is 33.

The square root of 21968511 is about 4687.0578191441. The cubic root of 21968511 is about 280.0701822372.

The spelling of 21968511 in words is "twenty-one million, nine hundred sixty-eight thousand, five hundred eleven".