191581981 has 2 divisors, whose sum is σ = 191581982. Its totient is φ = 191581980.

The previous prime is 191581963. The next prime is 191582047. The reversal of 191581981 is 189185191.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 115369081 + 76212900 = 10741^2 + 8730^2 .

It is a cyclic number.

It is not a de Polignac number, because 191581981 - 2¹¹ = 191579933 is a prime.

It is a super-2 number, since 2×191581981² = 73407310887768722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (191581931) 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, 95790990 + 95790991.

It is an arithmetic number, because the mean of its divisors is an integer number (95790991).

Almost surely, 2^191581981 is an apocalyptic number.

It is an amenable number.

191581981 is a deficient number, since it is larger than the sum of its proper divisors (1).

191581981 is an equidigital number, since it uses as much as digits as its factorization.

191581981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 25920, while the sum is 43.

The square root of 191581981 is about 13841.3142800819. The cubic root of 191581981 is about 576.4808518832.

The spelling of 191581981 in words is "one hundred ninety-one million, five hundred eighty-one thousand, nine hundred eighty-one".