81861019 has 4 divisors (see below), whose sum is σ = 81925720. Its totient is φ = 81796320.

The previous prime is 81861011. The next prime is 81861029. The reversal of 81861019 is 91016818.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81861019 - 2³ = 81861011 is a prime.

It is a super-2 number, since 2×81861019² = 13402452863436722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81861011) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 30414 + ... + 32995.

It is an arithmetic number, because the mean of its divisors is an integer number (20481430).

Almost surely, 2^81861019 is an apocalyptic number.

81861019 is a deficient number, since it is larger than the sum of its proper divisors (64701).

81861019 is a wasteful number, since it uses less digits than its factorization.

81861019 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 64700.

The product of its (nonzero) digits is 3456, while the sum is 34.

The square root of 81861019 is about 9047.7079417939. The cubic root of 81861019 is about 434.2025624679.

The spelling of 81861019 in words is "eighty-one million, eight hundred sixty-one thousand, nineteen".