81136521 has 6 divisors (see below), whose sum is σ = 117197210. Its totient is φ = 54091008.

The previous prime is 81136511. The next prime is 81136537. The reversal of 81136521 is 12563118.

81136521 is a `hidden beast` number, since 8 + 1 + 1 + 3 + 652 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 80353296 + 783225 = 8964^2 + 885^2 .

It is not a de Polignac number, because 81136521 - 2¹⁰ = 81135497 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81136511) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4507576 + ... + 4507593.

Almost surely, 2^81136521 is an apocalyptic number.

It is an amenable number.

81136521 is a deficient number, since it is larger than the sum of its proper divisors (36060689).

81136521 is a wasteful number, since it uses less digits than its factorization.

81136521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9015175 (or 9015172 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 81136521 is about 9007.5813068770. The cubic root of 81136521 is about 432.9178178048.

Adding to 81136521 its reverse (12563118), we get a palindrome (93699639).

The spelling of 81136521 in words is "eighty-one million, one hundred thirty-six thousand, five hundred twenty-one".