21233665 has 8 divisors (see below), whose sum is σ = 25513128. Its totient is φ = 16965120.

The previous prime is 21233651. The next prime is 21233689. The reversal of 21233665 is 56633212.

It is a Cunningham number, because it is equal to 4608²+1.

It can be written as a sum of positive squares in 4 ways, for example, as 1 + 21233664 = 1^2 + 4608^2 .

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

It is not a de Polignac number, because 21233665 - 2⁵ = 21233633 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2449 + ... + 6961.

It is an arithmetic number, because the mean of its divisors is an integer number (3189141).

It is a Proth number, since it is equal to 81 ⋅ 2¹⁸ + 1 and 81 < 2¹⁸.

Almost surely, 2^21233665 is an apocalyptic number.

It is an amenable number.

21233665 is a deficient number, since it is larger than the sum of its proper divisors (4279463).

21233665 is an equidigital number, since it uses as much as digits as its factorization.

21233665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5459.

The product of its digits is 6480, while the sum is 28.

The square root of 21233665 is about 4608.0001085069. Note that the first 3 decimals coincide. The cubic root of 21233665 is about 276.9119218461.

Adding to 21233665 its reverse (56633212), we get a palindrome (77866877).

The spelling of 21233665 in words is "twenty-one million, two hundred thirty-three thousand, six hundred sixty-five".