81851989 has 4 divisors (see below), whose sum is σ = 82038880. Its totient is φ = 81665100.

The previous prime is 81851983. The next prime is 81852011. The reversal of 81851989 is 98915818.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 98915818 = 2 ⋅49457909.

It is a cyclic number.

It is not a de Polignac number, because 81851989 - 2²³ = 73463381 is a prime.

It is a super-2 number, since 2×81851989² = 13399496206512242, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81851983) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 92787 + ... + 93664.

It is an arithmetic number, because the mean of its divisors is an integer number (20509720).

Almost surely, 2^81851989 is an apocalyptic number.

It is an amenable number.

81851989 is a deficient number, since it is larger than the sum of its proper divisors (186891).

81851989 is a wasteful number, since it uses less digits than its factorization.

81851989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 186890.

The product of its digits is 207360, while the sum is 49.

The square root of 81851989 is about 9047.2089066187. The cubic root of 81851989 is about 434.1865964100.

The spelling of 81851989 in words is "eighty-one million, eight hundred fifty-one thousand, nine hundred eighty-nine".