81991141 has 2 divisors, whose sum is σ = 81991142. Its totient is φ = 81991140.

The previous prime is 81991127. The next prime is 81991157. The reversal of 81991141 is 14119918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81540900 + 450241 = 9030^2 + 671^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81991141 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81991097 and 81991106.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81991121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40995570 + 40995571.

It is an arithmetic number, because the mean of its divisors is an integer number (40995571).

Almost surely, 2^81991141 is an apocalyptic number.

It is an amenable number.

81991141 is a deficient number, since it is larger than the sum of its proper divisors (1).

81991141 is an equidigital number, since it uses as much as digits as its factorization.

81991141 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2592, while the sum is 34.

The square root of 81991141 is about 9054.8959684803. The cubic root of 81991141 is about 434.4325025819.

The spelling of 81991141 in words is "eighty-one million, nine hundred ninety-one thousand, one hundred forty-one".