21947081 has 4 divisors (see below), whose sum is σ = 23635332. Its totient is φ = 20258832.

The previous prime is 21947077. The next prime is 21947089. The reversal of 21947081 is 18074912.

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

It can be written as a sum of positive squares in 2 ways, for example, as 3534400 + 18412681 = 1880^2 + 4291^2 .

It is a cyclic number.

It is not a de Polignac number, because 21947081 - 2² = 21947077 is a prime.

It is a super-2 number, since 2×21947081² = 963348728841122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21947089) 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 3 ways as a sum of consecutive naturals, for example, 844106 + ... + 844131.

It is an arithmetic number, because the mean of its divisors is an integer number (5908833).

Almost surely, 2^21947081 is an apocalyptic number.

It is an amenable number.

21947081 is a deficient number, since it is larger than the sum of its proper divisors (1688251).

21947081 is a wasteful number, since it uses less digits than its factorization.

21947081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1688250.

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 21947081 is about 4684.7711790439. The cubic root of 21947081 is about 279.9790843220.

The spelling of 21947081 in words is "twenty-one million, nine hundred forty-seven thousand, eighty-one".