81861869 has 2 divisors, whose sum is σ = 81861870. Its totient is φ = 81861868.

The previous prime is 81861803. The next prime is 81861877. The reversal of 81861869 is 96816818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 79887844 + 1974025 = 8938^2 + 1405^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81861869 is a prime.

It is a super-2 number, since 2×81861869² = 13402731192346322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81861569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40930934 + 40930935.

It is an arithmetic number, because the mean of its divisors is an integer number (40930935).

Almost surely, 2^81861869 is an apocalyptic number.

It is an amenable number.

81861869 is a deficient number, since it is larger than the sum of its proper divisors (1).

81861869 is an equidigital number, since it uses as much as digits as its factorization.

81861869 is an evil number, because the sum of its binary digits is even.

The product of its digits is 165888, while the sum is 47.

The square root of 81861869 is about 9047.7549148946. The cubic root of 81861869 is about 434.2040653032.

The spelling of 81861869 in words is "eighty-one million, eight hundred sixty-one thousand, eight hundred sixty-nine".