21306881 has 2 divisors, whose sum is σ = 21306882. Its totient is φ = 21306880.

The previous prime is 21306869. The next prime is 21306913. The reversal of 21306881 is 18860312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14753281 + 6553600 = 3841^2 + 2560^2 .

It is a cyclic number.

It is not a de Polignac number, because 21306881 - 2¹⁰ = 21305857 is a prime.

It is a super-2 number, since 2×21306881² = 907966355896322, 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 (21306811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10653440 + 10653441.

It is an arithmetic number, because the mean of its divisors is an integer number (10653441).

Almost surely, 2^21306881 is an apocalyptic number.

It is an amenable number.

21306881 is a deficient number, since it is larger than the sum of its proper divisors (1).

21306881 is an equidigital number, since it uses as much as digits as its factorization.

21306881 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 21306881 is about 4615.9377162176. The cubic root of 21306881 is about 277.2298309312.

The spelling of 21306881 in words is "twenty-one million, three hundred six thousand, eight hundred eighty-one".