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21390 = 2352331

21390 has 32 divisors (see below), whose sum is σ = 55296. Its totient is φ = 5280.

The previous prime is 21383. The next prime is 21391. The reversal of 21390 is 9312.

21390 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a nialpdrome in base 13 and base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391) by changing a digit.

21390 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 15 ways as a sum of consecutive naturals, for example, 675 + ... + 705.

It is an arithmetic number, because the mean of its divisors is an integer number (1728).

221390 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21390, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27648).

21390 is an abundant number, since it is smaller than the sum of its proper divisors (33906).

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

21390 is a wasteful number, since it uses less digits than its factorization.

21390 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 64.

The product of its (nonzero) digits is 54, while the sum is 15.

The square root of 21390 is about 146.2532050931. The cubic root of 21390 is about 27.7589858084.

It can be divided in two parts, 213 and 90, that added together give a palindrome (303).

The spelling of 21390 in words is "twenty-one thousand, three hundred ninety".

Divisors: 1 2 3 5 6 10 15 23 30 31 46 62 69 93 115 138 155 186 230 310 345 465 690 713 930 1426 2139 3565 4278 7130 10695 21390