81525509 has 4 divisors (see below), whose sum is σ = 87796716. Its totient is φ = 75254304.

The previous prime is 81525497. The next prime is 81525511. The reversal of 81525509 is 90552518.

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 30360100 + 51165409 = 5510^2 + 7153^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81525509 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 (81525539) 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, 3135584 + ... + 3135609.

It is an arithmetic number, because the mean of its divisors is an integer number (21949179).

Almost surely, 2^81525509 is an apocalyptic number.

It is an amenable number.

81525509 is a deficient number, since it is larger than the sum of its proper divisors (6271207).

81525509 is a wasteful number, since it uses less digits than its factorization.

81525509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6271206.

The product of its (nonzero) digits is 18000, while the sum is 35.

The square root of 81525509 is about 9029.1477449425. The cubic root of 81525509 is about 433.6085525159.

The spelling of 81525509 in words is "eighty-one million, five hundred twenty-five thousand, five hundred nine".