81505871 has 4 divisors (see below), whose sum is σ = 86300352. Its totient is φ = 76711392.

The previous prime is 81505867. The next prime is 81505901. The reversal of 81505871 is 17850518.

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 81505871 - 2² = 81505867 is a prime.

It is a Duffinian number.

It is a plaindrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81505811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2397215 + ... + 2397248.

It is an arithmetic number, because the mean of its divisors is an integer number (21575088).

Almost surely, 2^81505871 is an apocalyptic number.

81505871 is a deficient number, since it is larger than the sum of its proper divisors (4794481).

81505871 is a wasteful number, since it uses less digits than its factorization.

81505871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4794480.

The product of its (nonzero) digits is 11200, while the sum is 35.

The square root of 81505871 is about 9028.0602013943. The cubic root of 81505871 is about 433.5737336039.

The spelling of 81505871 in words is "eighty-one million, five hundred five thousand, eight hundred seventy-one".