21981011 has 4 divisors (see below), whose sum is σ = 23671872. Its totient is φ = 20290152.

The previous prime is 21980999. The next prime is 21981013. The reversal of 21981011 is 11018912.

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 21981011 - 2⁶ = 21980947 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21981013) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 845411 + ... + 845436.

It is an arithmetic number, because the mean of its divisors is an integer number (5917968).

Almost surely, 2^21981011 is an apocalyptic number.

21981011 is a deficient number, since it is larger than the sum of its proper divisors (1690861).

21981011 is a wasteful number, since it uses less digits than its factorization.

21981011 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1690860.

The product of its (nonzero) digits is 144, while the sum is 23.

The square root of 21981011 is about 4688.3910886358. The cubic root of 21981011 is about 280.1232917917.

Adding to 21981011 its reverse (11018912), we get a palindrome (32999923).

The spelling of 21981011 in words is "twenty-one million, nine hundred eighty-one thousand, eleven".