21135680 has 42 divisors (see below), whose sum is σ = 50525934. Its totient is φ = 8421376.

The previous prime is 21135677. The next prime is 21135683. The reversal of 21135680 is 8653112.

It is an interprime number because it is at equal distance from previous prime (21135677) and next prime (21135683).

It can be written as a sum of positive squares in 3 ways, for example, as 14622976 + 6512704 = 3824^2 + 2552^2 .

It is a zygodrome in base 4.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21135683) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 82112 + ... + 82368.

Almost surely, 2^21135680 is an apocalyptic number.

21135680 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 21135680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25262967).

21135680 is an abundant number, since it is smaller than the sum of its proper divisors (29390254).

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

21135680 is an frugal number, since it uses more digits than its factorization.

21135680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 531 (or 264 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 26.

The square root of 21135680 is about 4597.3557617396. The cubic root of 21135680 is about 276.4853184884.

Adding to 21135680 its reverse (8653112), we get a palindrome (29788792).

The spelling of 21135680 in words is "twenty-one million, one hundred thirty-five thousand, six hundred eighty".