81994181 has 2 divisors, whose sum is σ = 81994182. Its totient is φ = 81994180.

The previous prime is 81994151. The next prime is 81994189. The reversal of 81994181 is 18149918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81993025 + 1156 = 9055^2 + 34^2 .

It is a cyclic number.

It is not a de Polignac number, because 81994181 - 2⁶ = 81994117 is a prime.

It is a super-2 number, since 2×81994181² = 13446091435721522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81994189) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40997090 + 40997091.

It is an arithmetic number, because the mean of its divisors is an integer number (40997091).

Almost surely, 2^81994181 is an apocalyptic number.

It is an amenable number.

81994181 is a deficient number, since it is larger than the sum of its proper divisors (1).

81994181 is an equidigital number, since it uses as much as digits as its factorization.

81994181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 41.

The square root of 81994181 is about 9055.0638319120. The cubic root of 81994181 is about 434.4378716924.

The spelling of 81994181 in words is "eighty-one million, nine hundred ninety-four thousand, one hundred eighty-one".