21568 has 14 divisors (see below), whose sum is σ = 42926. Its totient is φ = 10752.
The previous prime is 21563. The next prime is 21569. The reversal of 21568 is 86512.
It is a happy number.
21568 is nontrivially palindromic in base 7.
It can be written as a sum of positive squares in only one way, i.e., 16384 + 5184 = 128^2 + 72^2 .
It is a nialpdrome in base 8 and base 16.
It is a zygodrome in base 7.
It is not an unprimeable number, because it can be changed into a prime (21563) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105 + ... + 232.
221568 is an apocalyptic number.
21568 is the 79-th centered heptagonal number.
It is an amenable number.
21568 is a deficient number, since it is larger than the sum of its proper divisors (21358).
21568 is an equidigital number, since it uses as much as digits as its factorization.
21568 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 349 (or 339 counting only the distinct ones).
The product of its digits is 480, while the sum is 22.
The square root of 21568 is about 146.8604780055. The cubic root of 21568 is about 27.8357733487.
It can be divided in two parts, 2 and 1568, that multiplied together give a square (3136 = 562).
The spelling of 21568 in words is "twenty-one thousand, five hundred sixty-eight".
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