21664281 has 8 divisors (see below), whose sum is σ = 28974304. Its totient is φ = 14398560.

The previous prime is 21664267. The next prime is 21664297. The reversal of 21664281 is 18246612.

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

It is not a de Polignac number, because 21664281 - 2¹⁵ = 21631513 is a prime.

It is a super-2 number, since 2×21664281² = 938682142493922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21664081) 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, 9916 + ... + 11901.

It is an arithmetic number, because the mean of its divisors is an integer number (3621788).

Almost surely, 2^21664281 is an apocalyptic number.

It is an amenable number.

21664281 is a deficient number, since it is larger than the sum of its proper divisors (7310023).

21664281 is a wasteful number, since it uses less digits than its factorization.

21664281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22151.

The product of its digits is 4608, while the sum is 30.

The square root of 21664281 is about 4654.4904124942. The cubic root of 21664281 is about 278.7713212056.

It can be divided in two parts, 21664 and 281, that added together give a triangular number (21945 = T₂₀₉).

The spelling of 21664281 in words is "twenty-one million, six hundred sixty-four thousand, two hundred eighty-one".