21081913 has 8 divisors (see below), whose sum is σ = 21732480. Its totient is φ = 20437920.

The previous prime is 21081901. The next prime is 21081919. The reversal of 21081913 is 31918012.

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

It is a cyclic number.

It is not a de Polignac number, because 21081913 - 2⁵ = 21081881 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21081919) 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 in 7 ways as a sum of consecutive naturals, for example, 5308 + ... + 8386.

It is an arithmetic number, because the mean of its divisors is an integer number (2716560).

Almost surely, 2^21081913 is an apocalyptic number.

It is an amenable number.

21081913 is a deficient number, since it is larger than the sum of its proper divisors (650567).

21081913 is a wasteful number, since it uses less digits than its factorization.

21081913 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3287.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 21081913 is about 4591.5044375455. The cubic root of 21081913 is about 276.2506693131.

Adding to 21081913 its reverse (31918012), we get a palindrome (52999925).

The spelling of 21081913 in words is "twenty-one million, eighty-one thousand, nine hundred thirteen".