21351660 has 144 divisors (see below), whose sum is σ = 69981408. Its totient is φ = 4843520.

The previous prime is 21351637. The next prime is 21351661. The reversal of 21351660 is 6615312.

It is a self number, because there is not a number n which added to its sum of digits gives 21351660.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21351661) by changing a digit.

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 47 ways as a sum of consecutive naturals, for example, 123334 + ... + 123506.

It is an arithmetic number, because the mean of its divisors is an integer number (485982).

Almost surely, 2^21351660 is an apocalyptic number.

21351660 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 21351660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34990704).

21351660 is an abundant number, since it is smaller than the sum of its proper divisors (48629748).

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

21351660 is a wasteful number, since it uses less digits than its factorization.

21351660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 224 (or 211 counting only the distinct ones).

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21351660 is about 4620.7856474846. The cubic root of 21351660 is about 277.4239057652.

Adding to 21351660 its reverse (6615312), we get a palindrome (27966972).

The spelling of 21351660 in words is "twenty-one million, three hundred fifty-one thousand, six hundred sixty".