81521306 has 4 divisors (see below), whose sum is σ = 122281962. Its totient is φ = 40760652.

The previous prime is 81521299. The next prime is 81521309. The reversal of 81521306 is 60312518.

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

It can be written as a sum of positive squares in only one way, i.e., 68740681 + 12780625 = 8291^2 + 3575^2 .

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81521309) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20380325 + ... + 20380328.

Almost surely, 2^81521306 is an apocalyptic number.

81521306 is a deficient number, since it is larger than the sum of its proper divisors (40760656).

81521306 is a wasteful number, since it uses less digits than its factorization.

81521306 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40760655.

The product of its (nonzero) digits is 1440, while the sum is 26.

The square root of 81521306 is about 9028.9149957235. The cubic root of 81521306 is about 433.6011009093.

The spelling of 81521306 in words is "eighty-one million, five hundred twenty-one thousand, three hundred six".