20729981 has 2 divisors, whose sum is σ = 20729982. Its totient is φ = 20729980.

The previous prime is 20729939. The next prime is 20729993. The reversal of 20729981 is 18992702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14945956 + 5784025 = 3866^2 + 2405^2 .

It is a cyclic number.

It is not a de Polignac number, because 20729981 - 2²² = 16535677 is a prime.

It is a super-2 number, since 2×20729981² = 859464224520722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20729281) 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 as a sum of consecutive naturals, namely, 10364990 + 10364991.

It is an arithmetic number, because the mean of its divisors is an integer number (10364991).

Almost surely, 2^20729981 is an apocalyptic number.

It is an amenable number.

20729981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20729981 is an equidigital number, since it uses as much as digits as its factorization.

20729981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 20729981 is about 4553.0188886057. The cubic root of 20729981 is about 274.7048337152.

The spelling of 20729981 in words is "twenty million, seven hundred twenty-nine thousand, nine hundred eighty-one".