20681 has 2 divisors, whose sum is σ = 20682. Its totient is φ = 20680.

The previous prime is 20663. The next prime is 20693. The reversal of 20681 is 18602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13456 + 7225 = 116^2 + 85^2 .

It is a cyclic number.

It is not a de Polignac number, because 20681 - 2¹⁴ = 4297 is a prime.

It is a super-2 number, since 2×20681² = 855407522, which contains 22 as substring.

It is a nialpdrome in base 12 and base 14.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 20681.

It is not a weakly prime, because it can be changed into another prime (20611) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10340 + 10341.

It is an arithmetic number, because the mean of its divisors is an integer number (10341).

2²⁰⁶⁸¹ is an apocalyptic number.

It is an amenable number.

20681 is a deficient number, since it is larger than the sum of its proper divisors (1).

20681 is an equidigital number, since it uses as much as digits as its factorization.

20681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 20681 is about 143.8089009763. The cubic root of 20681 is about 27.4488304672.

The spelling of 20681 in words is "twenty thousand, six hundred eighty-one".