21510 has 24 divisors (see below), whose sum is σ = 56160.
Its totient is φ = 5712.
The previous prime is 21503. The next prime is 21517. The reversal of 21510 is 1512.
It can be divided in two parts, 215 and 10, that added together give a square (225 = 152).
It is a happy number.
It is an interprime number because it is at equal distance from previous prime (21503) and next prime (21517).
It is a Harshad number since it is a multiple of its sum of digits (9).
It is a junction number, because it is equal to n+sod(n) for n = 21492 and 21501.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (21517) by changing a digit.
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 11 ways as a sum of consecutive naturals, for example, 30 + ... + 209.
It is an arithmetic number, because the mean of its divisors is an integer number (2340).
221510 is an apocalyptic number.
21510 is an abundant number, since it is smaller than the sum of its proper divisors (34650).
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 (28080).
21510 is a wasteful number, since it uses less digits than its factorization.
21510 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 252 (or 249 counting only the distinct ones).
The product of its (nonzero) digits is 10, while the sum is 9.
The square root of 21510 is about 146.6628787390.
The cubic root of 21510 is about 27.8107992479.
The spelling of 21510 in words is "twenty-one thousand, five hundred ten".