20681665 has 4 divisors (see below), whose sum is σ = 24818004. Its totient is φ = 16545328.

The previous prime is 20681663. The next prime is 20681701. The reversal of 20681665 is 56618602.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14311089 + 6370576 = 3783^2 + 2524^2 .

It is a cyclic number.

It is not a de Polignac number, because 20681665 - 2¹ = 20681663 is a prime.

It is a super-3 number, since 3×20681665³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20681665.

It is not an unprimeable number, because it can be changed into a prime (20681663) 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 3 ways as a sum of consecutive naturals, for example, 2068162 + ... + 2068171.

It is an arithmetic number, because the mean of its divisors is an integer number (6204501).

Almost surely, 2^20681665 is an apocalyptic number.

It is an amenable number.

20681665 is a deficient number, since it is larger than the sum of its proper divisors (4136339).

20681665 is an equidigital number, since it uses as much as digits as its factorization.

20681665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4136338.

The product of its (nonzero) digits is 17280, while the sum is 34.

The square root of 20681665 is about 4547.7098632169. The cubic root of 20681665 is about 274.4912467086.

The spelling of 20681665 in words is "twenty million, six hundred eighty-one thousand, six hundred sixty-five".