21309081 has 8 divisors (see below), whose sum is σ = 28693824. Its totient is φ = 14065200.

The previous prime is 21309061. The next prime is 21309103. The reversal of 21309081 is 18090312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21309081 - 2⁷ = 21308953 is a prime.

It is a super-2 number, since 2×21309081² = 908153866129122, which contains 22 as substring.

It is a Smith number, since the sum of its digits (24) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (21309061) 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 in 7 ways as a sum of consecutive naturals, for example, 34861 + ... + 35466.

It is an arithmetic number, because the mean of its divisors is an integer number (3586728).

Almost surely, 2^21309081 is an apocalyptic number.

It is an amenable number.

21309081 is a deficient number, since it is larger than the sum of its proper divisors (7384743).

21309081 is a wasteful number, since it uses less digits than its factorization.

21309081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70431.

The product of its (nonzero) digits is 432, while the sum is 24.

The square root of 21309081 is about 4616.1760148417. The cubic root of 21309081 is about 277.2393722094.

Adding to 21309081 its reverse (18090312), we get a palindrome (39399393).

It can be divided in two parts, 2130 and 9081, that added together give a palindrome (11211).

The spelling of 21309081 in words is "twenty-one million, three hundred nine thousand, eighty-one".