21966 has 16 divisors (see below), whose sum is σ = 50304. Its totient is φ = 6264.

The previous prime is 21961. The next prime is 21977. The reversal of 21966 is 66912.

21966 is nontrivially palindromic in base 13.

It is a Curzon number.

It is a plaindrome in base 11 and base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21961) 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, 220 + ... + 303.

It is an arithmetic number, because the mean of its divisors is an integer number (3144).

2²¹⁹⁶⁶ is an apocalyptic number.

21966 is an abundant number, since it is smaller than the sum of its proper divisors (28338).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25152).

21966 is a wasteful number, since it uses less digits than its factorization.

21966 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 535.

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

The square root of 21966 is about 148.2093114484. The cubic root of 21966 is about 28.0059511160.

The spelling of 21966 in words is "twenty-one thousand, nine hundred sixty-six".