81387557 has 4 divisors (see below), whose sum is σ = 81405996. Its totient is φ = 81369120.

The previous prime is 81387487. The next prime is 81387571. The reversal of 81387557 is 75578318.

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 2515396 + 78872161 = 1586^2 + 8881^2 .

It is a cyclic number.

It is not a de Polignac number, because 81387557 - 2¹⁰ = 81386533 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81387577) 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, 1763 + ... + 12879.

It is an arithmetic number, because the mean of its divisors is an integer number (20351499).

Almost surely, 2^81387557 is an apocalyptic number.

It is an amenable number.

81387557 is a deficient number, since it is larger than the sum of its proper divisors (18439).

81387557 is a wasteful number, since it uses less digits than its factorization.

81387557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18438.

The product of its digits is 235200, while the sum is 44.

The square root of 81387557 is about 9021.5052513425. The cubic root of 81387557 is about 433.3638399956.

The spelling of 81387557 in words is "eighty-one million, three hundred eighty-seven thousand, five hundred fifty-seven".