21330581 has 2 divisors, whose sum is σ = 21330582. Its totient is φ = 21330580.

The previous prime is 21330503. The next prime is 21330593. The reversal of 21330581 is 18503312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12716356 + 8614225 = 3566^2 + 2935^2 .

It is a cyclic number.

It is not a de Polignac number, because 21330581 - 2¹⁰ = 21329557 is a prime.

It is a super-2 number, since 2×21330581² = 909987371595122, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21330481) 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, 10665290 + 10665291.

It is an arithmetic number, because the mean of its divisors is an integer number (10665291).

Almost surely, 2^21330581 is an apocalyptic number.

It is an amenable number.

21330581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21330581 is an equidigital number, since it uses as much as digits as its factorization.

21330581 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21330581 is about 4618.5041950831. The cubic root of 21330581 is about 277.3325819689.

Adding to 21330581 its reverse (18503312), we get a palindrome (39833893).

The spelling of 21330581 in words is "twenty-one million, three hundred thirty thousand, five hundred eighty-one".