21105680 has 20 divisors (see below), whose sum is σ = 49070892. Its totient is φ = 8442240.

The previous prime is 21105677. The next prime is 21105683. The reversal of 21105680 is 8650112.

It is an interprime number because it is at equal distance from previous prime (21105677) and next prime (21105683).

It can be written as a sum of positive squares in 2 ways, for example, as 14714896 + 6390784 = 3836^2 + 2528^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is not an unprimeable number, because it can be changed into a prime (21105683) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 131831 + ... + 131990.

Almost surely, 2^21105680 is an apocalyptic number.

21105680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21105680 is an abundant number, since it is smaller than the sum of its proper divisors (27965212).

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

21105680 is a wasteful number, since it uses less digits than its factorization.

21105680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 263834 (or 263828 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 23.

The square root of 21105680 is about 4594.0918580281. The cubic root of 21105680 is about 276.3544420575.

Adding to 21105680 its reverse (8650112), we get a palindrome (29755792).

The spelling of 21105680 in words is "twenty-one million, one hundred five thousand, six hundred eighty".