21240881 has 2 divisors, whose sum is σ = 21240882. Its totient is φ = 21240880.

The previous prime is 21240833. The next prime is 21240887. The reversal of 21240881 is 18804212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19280881 + 1960000 = 4391^2 + 1400^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21240881 is a prime.

It is a super-2 number, since 2×21240881² = 902350051312322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21240881.

It is not a weakly prime, because it can be changed into another prime (21240887) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10620440 + 10620441.

It is an arithmetic number, because the mean of its divisors is an integer number (10620441).

Almost surely, 2^21240881 is an apocalyptic number.

It is an amenable number.

21240881 is a deficient number, since it is larger than the sum of its proper divisors (1).

21240881 is an equidigital number, since it uses as much as digits as its factorization.

21240881 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1024, while the sum is 26.

The square root of 21240881 is about 4608.7830280889. The cubic root of 21240881 is about 276.9432866641.

The spelling of 21240881 in words is "twenty-one million, two hundred forty thousand, eight hundred eighty-one".