21380081 has 2 divisors, whose sum is σ = 21380082. Its totient is φ = 21380080.

The previous prime is 21380071. The next prime is 21380113. The reversal of 21380081 is 18008312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20205025 + 1175056 = 4495^2 + 1084^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21380081 is a prime.

It is a super-2 number, since 2×21380081² = 914215727133122, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21380011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690040 + 10690041.

It is an arithmetic number, because the mean of its divisors is an integer number (10690041).

Almost surely, 2^21380081 is an apocalyptic number.

It is an amenable number.

21380081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21380081 is an equidigital number, since it uses as much as digits as its factorization.

21380081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 384, while the sum is 23.

The square root of 21380081 is about 4623.8599676028. The cubic root of 21380081 is about 277.5469433340.

Adding to 21380081 its reverse (18008312), we get a palindrome (39388393).

The spelling of 21380081 in words is "twenty-one million, three hundred eighty thousand, eighty-one".