21735210 has 128 divisors (see below), whose sum is σ = 63866880. Its totient is φ = 4628736.

The previous prime is 21735209. The next prime is 21735223. The reversal of 21735210 is 1253712.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 261829 + ... + 261911.

It is an arithmetic number, because the mean of its divisors is an integer number (498960).

Almost surely, 2^21735210 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21735210, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31933440).

21735210 is an abundant number, since it is smaller than the sum of its proper divisors (42131670).

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

21735210 is a wasteful number, since it uses less digits than its factorization.

21735210 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 172.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21735210 is about 4662.1036024524. The cubic root of 21735210 is about 279.0752228407.

Adding to 21735210 its reverse (1253712), we get a palindrome (22988922).

It can be divided in two parts, 21735 and 210, that added together give a triangular number (21945 = T₂₀₉).

The spelling of 21735210 in words is "twenty-one million, seven hundred thirty-five thousand, two hundred ten".