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21080 = 2351731

21080 has 32 divisors (see below), whose sum is σ = 51840. Its totient is φ = 7680.

The previous prime is 21067. The next prime is 21089. The reversal of 21080 is 8012.

21080 is an undulating number in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21089) by changing a digit.

21080 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 665 + ... + 695.

It is an arithmetic number, because the mean of its divisors is an integer number (1620).

221080 is an apocalyptic number.

21080 is a gapful number since it is divisible by the number (20) 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 21080, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25920).

21080 is an abundant number, since it is smaller than the sum of its proper divisors (30760).

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

21080 is a wasteful number, since it uses less digits than its factorization.

21080 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59 (or 55 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 21080 is about 145.1895313031. The cubic root of 21080 is about 27.6242313280.

Adding to 21080 its reverse (8012), we get a palindrome (29092).

The spelling of 21080 in words is "twenty-one thousand, eighty".

Divisors: 1 2 4 5 8 10 17 20 31 34 40 62 68 85 124 136 155 170 248 310 340 527 620 680 1054 1240 2108 2635 4216 5270 10540 21080