21318881 has 2 divisors, whose sum is σ = 21318882. Its totient is φ = 21318880.

The previous prime is 21318877. The next prime is 21318889. The reversal of 21318881 is 18881312.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20611600 + 707281 = 4540^2 + 841^2 .

It is a cyclic number.

It is not a de Polignac number, because 21318881 - 2² = 21318877 is a prime.

It is a super-2 number, since 2×21318881² = 908989374184322, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21318889) 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 as a sum of consecutive naturals, namely, 10659440 + 10659441.

It is an arithmetic number, because the mean of its divisors is an integer number (10659441).

Almost surely, 2^21318881 is an apocalyptic number.

It is an amenable number.

21318881 is a deficient number, since it is larger than the sum of its proper divisors (1).

21318881 is an equidigital number, since it uses as much as digits as its factorization.

21318881 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3072, while the sum is 32.

The square root of 21318881 is about 4617.2373774802. The cubic root of 21318881 is about 277.2818662905.

The spelling of 21318881 in words is "twenty-one million, three hundred eighteen thousand, eight hundred eighty-one".