21307281 has 8 divisors (see below), whose sum is σ = 28627104. Its totient is φ = 14096160.

The previous prime is 21307271. The next prime is 21307283. The reversal of 21307281 is 18270312.

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

It is not a de Polignac number, because 21307281 - 2¹⁸ = 21045137 is a prime.

It is a super-2 number, since 2×21307281² = 908000447225922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21307283) 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, 26716 + ... + 27501.

It is an arithmetic number, because the mean of its divisors is an integer number (3578388).

Almost surely, 2^21307281 is an apocalyptic number.

It is an amenable number.

21307281 is a deficient number, since it is larger than the sum of its proper divisors (7319823).

21307281 is a wasteful number, since it uses less digits than its factorization.

21307281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54351.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21307281 is about 4615.9810441552. The cubic root of 21307281 is about 277.2315657579.

Adding to 21307281 its reverse (18270312), we get a palindrome (39577593).

The spelling of 21307281 in words is "twenty-one million, three hundred seven thousand, two hundred eighty-one".