81660447 has 16 divisors (see below), whose sum is σ = 131976960. Its totient is φ = 49491000.

The previous prime is 81660427. The next prime is 81660457. The reversal of 81660447 is 74406618.

81660447 is a `hidden beast` number, since 8 + 1 + 6 + 604 + 47 = 666.

It is a de Polignac number, because none of the positive numbers 2^k-81660447 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81660407) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 137179 + ... + 137772.

It is an arithmetic number, because the mean of its divisors is an integer number (8248560).

Almost surely, 2^81660447 is an apocalyptic number.

81660447 is a deficient number, since it is larger than the sum of its proper divisors (50316513).

81660447 is a wasteful number, since it uses less digits than its factorization.

81660447 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 274971 (or 274965 counting only the distinct ones).

The product of its (nonzero) digits is 32256, while the sum is 36.

The square root of 81660447 is about 9036.6170108066. The cubic root of 81660447 is about 433.8476515819.

The spelling of 81660447 in words is "eighty-one million, six hundred sixty thousand, four hundred forty-seven".