21145981 has 8 divisors (see below), whose sum is σ = 22224224. Its totient is φ = 20094480.

The previous prime is 21145979. The next prime is 21145987. The reversal of 21145981 is 18954112.

It is a happy number.

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 21145981 - 2¹ = 21145979 is a prime.

It is a super-3 number, since 3×21145981³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21145987) 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, 5055 + ... + 8236.

It is an arithmetic number, because the mean of its divisors is an integer number (2778028).

Almost surely, 2^21145981 is an apocalyptic number.

It is an amenable number.

21145981 is a deficient number, since it is larger than the sum of its proper divisors (1078243).

21145981 is a wasteful number, since it uses less digits than its factorization.

21145981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13371.

The product of its digits is 2880, while the sum is 31.

The square root of 21145981 is about 4598.4759431794. The cubic root of 21145981 is about 276.5302285283.

The spelling of 21145981 in words is "twenty-one million, one hundred forty-five thousand, nine hundred eighty-one".