21680361 has 12 divisors (see below), whose sum is σ = 31491460. Its totient is φ = 14372640.

The previous prime is 21680353. The next prime is 21680381. The reversal of 21680361 is 16308612.

It can be written as a sum of positive squares in 2 ways, for example, as 197136 + 21483225 = 444^2 + 4635^2 .

It is not a de Polignac number, because 21680361 - 2³ = 21680353 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21680341) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5026 + ... + 8283.

Almost surely, 2^21680361 is an apocalyptic number.

It is an amenable number.

21680361 is a deficient number, since it is larger than the sum of its proper divisors (9811099).

21680361 is a wasteful number, since it uses less digits than its factorization.

21680361 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13496 (or 13493 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21680361 is about 4656.2174562621. The cubic root of 21680361 is about 278.8402754786.

Adding to 21680361 its reverse (16308612), we get a palindrome (37988973).

The spelling of 21680361 in words is "twenty-one million, six hundred eighty thousand, three hundred sixty-one".