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21968 has 10 divisors (see below), whose sum is σ = 42594. Its totient is φ = 10976.

The previous prime is 21961. The next prime is 21977. The reversal of 21968 is 86912.

It can be written as a sum of positive squares in only one way, i.e., 21904 + 64 = 148^2 + 8^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21961) by changing a digit.

21968 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 as a sum of consecutive naturals, namely, 671 + ... + 702.

221968 is an apocalyptic number.

It is an amenable number.

21968 is a deficient number, since it is larger than the sum of its proper divisors (20626).

21968 is a wasteful number, since it uses less digits than its factorization.

21968 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1381 (or 1375 counting only the distinct ones).

The product of its digits is 864, while the sum is 26.

The square root of 21968 is about 148.2160585092. The cubic root of 21968 is about 28.0068010690.

It can be divided in two parts, 21 and 968, that added together give a palindrome (989).

The spelling of 21968 in words is "twenty-one thousand, nine hundred sixty-eight".

Divisors: 1 2 4 8 16 1373 2746 5492 10984 21968