20720681 has 2 divisors, whose sum is σ = 20720682. Its totient is φ = 20720680.

The previous prime is 20720653. The next prime is 20720717. The reversal of 20720681 is 18602702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13075456 + 7645225 = 3616^2 + 2765^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20720681 is a prime.

It is a super-2 number, since 2×20720681² = 858693242207522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 20720681.

It is not a weakly prime, because it can be changed into another prime (20720611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10360340 + 10360341.

It is an arithmetic number, because the mean of its divisors is an integer number (10360341).

Almost surely, 2^20720681 is an apocalyptic number.

It is an amenable number.

20720681 is a deficient number, since it is larger than the sum of its proper divisors (1).

20720681 is an equidigital number, since it uses as much as digits as its factorization.

20720681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 20720681 is about 4551.9974736373. The cubic root of 20720681 is about 274.6637476976.

The spelling of 20720681 in words is "twenty million, seven hundred twenty thousand, six hundred eighty-one".