21996 has 36 divisors (see below), whose sum is σ = 61152. Its totient is φ = 6624.

The previous prime is 21991. The next prime is 21997. The reversal of 21996 is 69912.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (36).

It is a nude number because it is divisible by every one of its digits.

It is not an unprimeable number, because it can be changed into a prime (21991) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 445 + ... + 491.

2²¹⁹⁹⁶ is an apocalyptic number.

21996 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21996, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30576).

21996 is an abundant number, since it is smaller than the sum of its proper divisors (39156).

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

21996 is a wasteful number, since it uses less digits than its factorization.

21996 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70 (or 65 counting only the distinct ones).

The product of its digits is 972, while the sum is 27.

The square root of 21996 is about 148.3104851317. The cubic root of 21996 is about 28.0186949980.

The spelling of 21996 in words is "twenty-one thousand, nine hundred ninety-six".