21281281 has 8 divisors (see below), whose sum is σ = 24350720. Its totient is φ = 18219168.

The previous prime is 21281261. The next prime is 21281321. The reversal of 21281281 is 18218212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21281281 - 2⁷ = 21281153 is a prime.

It is a super-2 number, since 2×21281281² = 905785842001922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21281201) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7765 + ... + 10141.

It is an arithmetic number, because the mean of its divisors is an integer number (3043840).

Almost surely, 2^21281281 is an apocalyptic number.

It is an amenable number.

21281281 is a deficient number, since it is larger than the sum of its proper divisors (3069439).

21281281 is a wasteful number, since it uses less digits than its factorization.

21281281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3663.

The product of its digits is 512, while the sum is 25.

The square root of 21281281 is about 4613.1638817627. The cubic root of 21281281 is about 277.1187568307.

Adding to 21281281 its reverse (18218212), we get a palindrome (39499493).

The spelling of 21281281 in words is "twenty-one million, two hundred eighty-one thousand, two hundred eighty-one".