21417281 has 4 divisors (see below), whose sum is σ = 21428100. Its totient is φ = 21406464.

The previous prime is 21417271. The next prime is 21417299. The reversal of 21417281 is 18271412.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 5216656 + 16200625 = 2284^2 + 4025^2 .

It is a cyclic number.

It is not a de Polignac number, because 21417281 - 2²² = 17222977 is a prime.

It is a super-2 number, since 2×21417281² = 917399850865922, which contains 22 as substring.

It is a Duffinian number.

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 21417281.

It is not an unprimeable number, because it can be changed into a prime (21417271) 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 in 3 ways as a sum of consecutive naturals, for example, 1496 + ... + 6713.

It is an arithmetic number, because the mean of its divisors is an integer number (5357025).

Almost surely, 2^21417281 is an apocalyptic number.

It is an amenable number.

21417281 is a deficient number, since it is larger than the sum of its proper divisors (10819).

21417281 is an equidigital number, since it uses as much as digits as its factorization.

21417281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10818.

The product of its digits is 896, while the sum is 26.

The square root of 21417281 is about 4627.8808325194. The cubic root of 21417281 is about 277.7078214887.

Adding to 21417281 its reverse (18271412), we get a palindrome (39688693).

The spelling of 21417281 in words is "twenty-one million, four hundred seventeen thousand, two hundred eighty-one".