21680245 has 8 divisors (see below), whose sum is σ = 26191800. Its totient is φ = 17227200.

The previous prime is 21680231. The next prime is 21680249. The reversal of 21680245 is 54208612.

It can be written as a sum of positive squares in 4 ways, for example, as 1258884 + 20421361 = 1122^2 + 4519^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21680245 - 2¹¹ = 21678197 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21680249) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13806 + ... + 15295.

It is an arithmetic number, because the mean of its divisors is an integer number (3273975).

Almost surely, 2^21680245 is an apocalyptic number.

It is an amenable number.

21680245 is a deficient number, since it is larger than the sum of its proper divisors (4511555).

21680245 is a wasteful number, since it uses less digits than its factorization.

21680245 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29255.

The product of its (nonzero) digits is 3840, while the sum is 28.

The square root of 21680245 is about 4656.2049997825. The cubic root of 21680245 is about 278.8397781694.

Adding to 21680245 its reverse (54208612), we get a palindrome (75888857).

The spelling of 21680245 in words is "twenty-one million, six hundred eighty thousand, two hundred forty-five".