20311981 has 2 divisors, whose sum is σ = 20311982. Its totient is φ = 20311980.

The previous prime is 20311979. The next prime is 20312021. The reversal of 20311981 is 18911302.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17089956 + 3222025 = 4134^2 + 1795^2 .

It is a cyclic number.

It is not a de Polignac number, because 20311981 - 2¹ = 20311979 is a prime.

It is a super-2 number, since 2×20311981² = 825153144288722, which contains 22 as substring.

Together with 20311979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20311901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10155990 + 10155991.

It is an arithmetic number, because the mean of its divisors is an integer number (10155991).

Almost surely, 2^20311981 is an apocalyptic number.

It is an amenable number.

20311981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20311981 is an equidigital number, since it uses as much as digits as its factorization.

20311981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 20311981 is about 4506.8815160818. The cubic root of 20311981 is about 272.8458969182.

The spelling of 20311981 in words is "twenty million, three hundred eleven thousand, nine hundred eighty-one".