21947917 has 4 divisors (see below), whose sum is σ = 21957696. Its totient is φ = 21938140.

The previous prime is 21947903. The next prime is 21947921. The reversal of 21947917 is 71974912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21947917 - 2²³ = 13559309 is a prime.

It is a super-2 number, since 2×21947917² = 963422121277778, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21947917.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21947977) 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, 348 + ... + 6634.

It is an arithmetic number, because the mean of its divisors is an integer number (5489424).

Almost surely, 2^21947917 is an apocalyptic number.

It is an amenable number.

21947917 is a deficient number, since it is larger than the sum of its proper divisors (9779).

21947917 is an equidigital number, since it uses as much as digits as its factorization.

21947917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9778.

The product of its digits is 31752, while the sum is 40.

The square root of 21947917 is about 4684.8604034699. The cubic root of 21947917 is about 279.9826392297.

The spelling of 21947917 in words is "twenty-one million, nine hundred forty-seven thousand, nine hundred seventeen".