21894581 has 2 divisors, whose sum is σ = 21894582. Its totient is φ = 21894580.

The previous prime is 21894571. The next prime is 21894583. The reversal of 21894581 is 18549812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21022225 + 872356 = 4585^2 + 934^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21894581 is a prime.

It is a super-2 number, since 2×21894581² = 958745354331122, which contains 22 as substring.

Together with 21894583, it forms a pair of twin primes.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21894583) 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 as a sum of consecutive naturals, namely, 10947290 + 10947291.

It is an arithmetic number, because the mean of its divisors is an integer number (10947291).

Almost surely, 2^21894581 is an apocalyptic number.

It is an amenable number.

21894581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21894581 is an equidigital number, since it uses as much as digits as its factorization.

21894581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23040, while the sum is 38.

The square root of 21894581 is about 4679.1645621842. The cubic root of 21894581 is about 279.7556584364.

The spelling of 21894581 in words is "twenty-one million, eight hundred ninety-four thousand, five hundred eighty-one".