21585281 has 2 divisors, whose sum is σ = 21585282. Its totient is φ = 21585280.

The previous prime is 21585271. The next prime is 21585283. The reversal of 21585281 is 18258512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16679056 + 4906225 = 4084^2 + 2215^2 .

It is a cyclic number.

It is not a de Polignac number, because 21585281 - 2²² = 17390977 is a prime.

It is a super-2 number, since 2×21585281² = 931848711697922, which contains 22 as substring.

Together with 21585283, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21585283) 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, 10792640 + 10792641.

It is an arithmetic number, because the mean of its divisors is an integer number (10792641).

Almost surely, 2^21585281 is an apocalyptic number.

It is an amenable number.

21585281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21585281 is an equidigital number, since it uses as much as digits as its factorization.

21585281 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6400, while the sum is 32.

The square root of 21585281 is about 4645.9962333175. The cubic root of 21585281 is about 278.4320568035.

The spelling of 21585281 in words is "twenty-one million, five hundred eighty-five thousand, two hundred eighty-one".