81509201 has 4 divisors (see below), whose sum is σ = 81708900. Its totient is φ = 81309504.

The previous prime is 81509191. The next prime is 81509231. The reversal of 81509201 is 10290518.

It is a happy number.

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 52940176 + 28569025 = 7276^2 + 5345^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81509201 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81509231) 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, 99236 + ... + 100053.

It is an arithmetic number, because the mean of its divisors is an integer number (20427225).

Almost surely, 2^81509201 is an apocalyptic number.

It is an amenable number.

81509201 is a deficient number, since it is larger than the sum of its proper divisors (199699).

81509201 is a wasteful number, since it uses less digits than its factorization.

81509201 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 199698.

The product of its (nonzero) digits is 720, while the sum is 26.

The square root of 81509201 is about 9028.2446245103. The cubic root of 81509201 is about 433.5796382128.

Adding to 81509201 its reverse (10290518), we get a palindrome (91799719).

The spelling of 81509201 in words is "eighty-one million, five hundred nine thousand, two hundred one".