81387505 has 4 divisors (see below), whose sum is σ = 97665012. Its totient is φ = 65110000.

The previous prime is 81387487. The next prime is 81387571. The reversal of 81387505 is 50578318.

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

It can be written as a sum of positive squares in 2 ways, for example, as 23155344 + 58232161 = 4812^2 + 7631^2 .

It is not a de Polignac number, because 81387505 - 2⁵ = 81387473 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8138746 + ... + 8138755.

It is an arithmetic number, because the mean of its divisors is an integer number (24416253).

Almost surely, 2^81387505 is an apocalyptic number.

It is an amenable number.

81387505 is a deficient number, since it is larger than the sum of its proper divisors (16277507).

81387505 is a wasteful number, since it uses less digits than its factorization.

81387505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16277506.

The product of its (nonzero) digits is 33600, while the sum is 37.

The square root of 81387505 is about 9021.5023693396. The cubic root of 81387505 is about 433.3637477009.

The spelling of 81387505 in words is "eighty-one million, three hundred eighty-seven thousand, five hundred five".