21668533 has 4 divisors (see below), whose sum is σ = 21679488. Its totient is φ = 21657580.

The previous prime is 21668519. The next prime is 21668593. The reversal of 21668533 is 33586612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21668533 - 2⁵ = 21668501 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21668593) 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, 1591 + ... + 6772.

It is an arithmetic number, because the mean of its divisors is an integer number (5419872).

Almost surely, 2^21668533 is an apocalyptic number.

It is an amenable number.

21668533 is a deficient number, since it is larger than the sum of its proper divisors (10955).

21668533 is an equidigital number, since it uses as much as digits as its factorization.

21668533 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10954.

The product of its digits is 25920, while the sum is 34.

The square root of 21668533 is about 4654.9471532983. The cubic root of 21668533 is about 278.7895579539.

It can be divided in two parts, 21668 and 533, that added together give a square (22201 = 149²).

The spelling of 21668533 in words is "twenty-one million, six hundred sixty-eight thousand, five hundred thirty-three".