81990197 has 2 divisors, whose sum is σ = 81990198. Its totient is φ = 81990196.

The previous prime is 81990179. The next prime is 81990199. The reversal of 81990197 is 79109918.

Together with previous prime (81990179) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81018001 + 972196 = 9001^2 + 986^2 .

It is a cyclic number.

It is not a de Polignac number, because 81990197 - 2²⁰ = 80941621 is a prime.

Together with 81990199, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81990199) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40995098 + 40995099.

It is an arithmetic number, because the mean of its divisors is an integer number (40995099).

Almost surely, 2^81990197 is an apocalyptic number.

It is an amenable number.

81990197 is a deficient number, since it is larger than the sum of its proper divisors (1).

81990197 is an equidigital number, since it uses as much as digits as its factorization.

81990197 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40824, while the sum is 44.

The square root of 81990197 is about 9054.8438418340. The cubic root of 81990197 is about 434.4308353048.

The spelling of 81990197 in words is "eighty-one million, nine hundred ninety thousand, one hundred ninety-seven".