21891937 has 4 divisors (see below), whose sum is σ = 23179716. Its totient is φ = 20604160.

The previous prime is 21891931. The next prime is 21891949. The reversal of 21891937 is 73919812.

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 7177041 + 14714896 = 2679^2 + 3836^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21891937 is a prime.

It is a super-2 number, since 2×21891937² = 958513811223938, 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 21891937.

It is not an unprimeable number, because it can be changed into a prime (21891931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 643864 + ... + 643897.

It is an arithmetic number, because the mean of its divisors is an integer number (5794929).

Almost surely, 2^21891937 is an apocalyptic number.

It is an amenable number.

21891937 is a deficient number, since it is larger than the sum of its proper divisors (1287779).

21891937 is a wasteful number, since it uses less digits than its factorization.

21891937 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1287778.

The product of its digits is 27216, while the sum is 40.

The square root of 21891937 is about 4678.8820245866. The cubic root of 21891937 is about 279.7443968410.

The spelling of 21891937 in words is "twenty-one million, eight hundred ninety-one thousand, nine hundred thirty-seven".