21311281 has 4 divisors (see below), whose sum is σ = 21358372. Its totient is φ = 21264192.

The previous prime is 21311261. The next prime is 21311347. The reversal of 21311281 is 18211312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12215025 + 9096256 = 3495^2 + 3016^2 .

It is a cyclic number.

It is not a de Polignac number, because 21311281 - 2⁵ = 21311249 is a prime.

It is a super-2 number, since 2×21311281² = 908341395721922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21311261) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22860 + ... + 23773.

It is an arithmetic number, because the mean of its divisors is an integer number (5339593).

Almost surely, 2^21311281 is an apocalyptic number.

It is an amenable number.

21311281 is a deficient number, since it is larger than the sum of its proper divisors (47091).

21311281 is an equidigital number, since it uses as much as digits as its factorization.

21311281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 47090.

The product of its digits is 96, while the sum is 19.

The square root of 21311281 is about 4616.4143011649. The cubic root of 21311281 is about 277.2489128309.

Adding to 21311281 its reverse (18211312), we get a palindrome (39522593).

The spelling of 21311281 in words is "twenty-one million, three hundred eleven thousand, two hundred eighty-one".