21921281 has 2 divisors, whose sum is σ = 21921282. Its totient is φ = 21921280.

The previous prime is 21921259. The next prime is 21921287. The reversal of 21921281 is 18212912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12673600 + 9247681 = 3560^2 + 3041^2 .

It is a cyclic number.

It is not a de Polignac number, because 21921281 - 2¹⁸ = 21659137 is a prime.

It is a super-2 number, since 2×21921281² = 961085121361922, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21921281.

It is not a weakly prime, because it can be changed into another prime (21921287) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10960640 + 10960641.

It is an arithmetic number, because the mean of its divisors is an integer number (10960641).

Almost surely, 2^21921281 is an apocalyptic number.

It is an amenable number.

21921281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21921281 is an equidigital number, since it uses as much as digits as its factorization.

21921281 is an evil number, because the sum of its binary digits is even.

The product of its digits is 576, while the sum is 26.

The square root of 21921281 is about 4682.0167663092. The cubic root of 21921281 is about 279.8693310364.

The spelling of 21921281 in words is "twenty-one million, nine hundred twenty-one thousand, two hundred eighty-one".