21685633 has 4 divisors (see below), whose sum is σ = 21712320. Its totient is φ = 21658948.

The previous prime is 21685621. The next prime is 21685661. The reversal of 21685633 is 33658612.

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.

It is a cyclic number.

It is not a de Polignac number, because 21685633 - 2⁹ = 21685121 is a prime.

It is a super-2 number, since 2×21685633² = 940533357221378, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21685603) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12085 + ... + 13762.

It is an arithmetic number, because the mean of its divisors is an integer number (5428080).

Almost surely, 2^21685633 is an apocalyptic number.

It is an amenable number.

21685633 is a deficient number, since it is larger than the sum of its proper divisors (26687).

21685633 is an equidigital number, since it uses as much as digits as its factorization.

21685633 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26686.

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

The square root of 21685633 is about 4656.7835466124. The cubic root of 21685633 is about 278.8628754527.

It can be divided in two parts, 216 and 85633, that added together give a square (85849 = 293²).

The spelling of 21685633 in words is "twenty-one million, six hundred eighty-five thousand, six hundred thirty-three".