21331281 has 32 divisors (see below), whose sum is σ = 31933440. Its totient is φ = 12602304.

The previous prime is 21331267. The next prime is 21331283. The reversal of 21331281 is 18213312.

It is not a de Polignac number, because 21331281 - 2⁶ = 21331217 is a prime.

It is a super-2 number, since 2×21331281² = 910047098201922, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21331283) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 69330 + ... + 69636.

It is an arithmetic number, because the mean of its divisors is an integer number (997920).

Almost surely, 2^21331281 is an apocalyptic number.

It is an amenable number.

21331281 is a deficient number, since it is larger than the sum of its proper divisors (10602159).

21331281 is a wasteful number, since it uses less digits than its factorization.

21331281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 405.

The product of its digits is 288, while the sum is 21.

The square root of 21331281 is about 4618.5799765729. The cubic root of 21331281 is about 277.3356156522.

Adding to 21331281 its reverse (18213312), we get a palindrome (39544593).

It can be divided in two parts, 21331 and 281, that added together give a palindrome (21612).

The spelling of 21331281 in words is "twenty-one million, three hundred thirty-one thousand, two hundred eighty-one".