81851789 has 2 divisors, whose sum is σ = 81851790. Its totient is φ = 81851788.

The previous prime is 81851743. The next prime is 81851827. The reversal of 81851789 is 98715818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 76825225 + 5026564 = 8765^2 + 2242^2 .

It is a cyclic number.

It is not a de Polignac number, because 81851789 - 2²⁰ = 80803213 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81841789) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40925894 + 40925895.

It is an arithmetic number, because the mean of its divisors is an integer number (40925895).

Almost surely, 2^81851789 is an apocalyptic number.

It is an amenable number.

81851789 is a deficient number, since it is larger than the sum of its proper divisors (1).

81851789 is an equidigital number, since it uses as much as digits as its factorization.

81851789 is an evil number, because the sum of its binary digits is even.

The product of its digits is 161280, while the sum is 47.

The square root of 81851789 is about 9047.1978534793. The cubic root of 81851789 is about 434.1862427741.

The spelling of 81851789 in words is "eighty-one million, eight hundred fifty-one thousand, seven hundred eighty-nine".