21669 has 8 divisors (see below), whose sum is σ = 29952. Its totient is φ = 13920.

The previous prime is 21661. The next prime is 21673. The reversal of 21669 is 96612.

21669 = 45² + 46² + ... + 53².

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

It is not a de Polignac number, because 21669 - 2³ = 21661 is a prime.

It is a super-2 number, since 2×21669² = 939091122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 24 + ... + 209.

It is an arithmetic number, because the mean of its divisors is an integer number (3744).

2²¹⁶⁶⁹ is an apocalyptic number.

It is an amenable number.

21669 is a deficient number, since it is larger than the sum of its proper divisors (8283).

21669 is a wasteful number, since it uses less digits than its factorization.

21669 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 267.

The product of its digits is 648, while the sum is 24.

The square root of 21669 is about 147.2039401647. The cubic root of 21669 is about 27.8791560763.

The spelling of 21669 in words is "twenty-one thousand, six hundred sixty-nine".