20817681 has 4 divisors (see below), whose sum is σ = 27756912. Its totient is φ = 13878452.

The previous prime is 20817677. The next prime is 20817701. The reversal of 20817681 is 18671802.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20817681 - 2² = 20817677 is a prime.

It is a super-2 number, since 2×20817681² = 866751684435522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (20817611) 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, 3469611 + ... + 3469616.

It is an arithmetic number, because the mean of its divisors is an integer number (6939228).

Almost surely, 2^20817681 is an apocalyptic number.

It is an amenable number.

20817681 is a deficient number, since it is larger than the sum of its proper divisors (6939231).

20817681 is an equidigital number, since it uses as much as digits as its factorization.

20817681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6939230.

The product of its (nonzero) digits is 5376, while the sum is 33.

The square root of 20817681 is about 4562.6396964915. The cubic root of 20817681 is about 275.0916763217.

The spelling of 20817681 in words is "twenty million, eight hundred seventeen thousand, six hundred eighty-one".