19891981 has 2 divisors, whose sum is σ = 19891982. Its totient is φ = 19891980.

The previous prime is 19891973. The next prime is 19892003. The reversal of 19891981 is 18919891.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19758025 + 133956 = 4445^2 + 366^2 .

It is an emirp because it is prime and its reverse (18919891) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19891981 - 2³ = 19891973 is a prime.

It is a super-2 number, since 2×19891981² = 791381816208722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19891961) 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, 9945990 + 9945991.

It is an arithmetic number, because the mean of its divisors is an integer number (9945991).

Almost surely, 2^19891981 is an apocalyptic number.

It is an amenable number.

19891981 is a deficient number, since it is larger than the sum of its proper divisors (1).

19891981 is an equidigital number, since it uses as much as digits as its factorization.

19891981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 46656, while the sum is 46.

The square root of 19891981 is about 4460.0427128000. The cubic root of 19891981 is about 270.9521981018.

The spelling of 19891981 in words is "nineteen million, eight hundred ninety-one thousand, nine hundred eighty-one".