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21028 = 227751

21028 has 12 divisors (see below), whose sum is σ = 42112. Its totient is φ = 9000.

The previous prime is 21023. The next prime is 21031. The reversal of 21028 is 82012.

21028 is an admirable number.

It is a junction number, because it is equal to n+sod(n) for n = 20999 and 21017.

It is not an unprimeable number, because it can be changed into a prime (21023) by changing a digit.

21028 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 (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 348 + ... + 403.

221028 is an apocalyptic number.

21028 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21028 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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 (21056).

21028 is a wasteful number, since it uses less digits than its factorization.

21028 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 762 (or 760 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21028 is about 145.0103444586. The cubic root of 21028 is about 27.6014982033.

The spelling of 21028 in words is "twenty-one thousand, twenty-eight".

Divisors: 1 2 4 7 14 28 751 1502 3004 5257 10514 21028