81681508 has 6 divisors (see below), whose sum is σ = 142942646. Its totient is φ = 40840752.

The previous prime is 81681493. The next prime is 81681511. The reversal of 81681508 is 80518618.

It can be written as a sum of positive squares in only one way, i.e., 46895104 + 34786404 = 6848^2 + 5898^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10210185 + ... + 10210192.

Almost surely, 2^81681508 is an apocalyptic number.

It is an amenable number.

81681508 is a deficient number, since it is larger than the sum of its proper divisors (61261138).

81681508 is a wasteful number, since it uses less digits than its factorization.

81681508 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20420381 (or 20420379 counting only the distinct ones).

The product of its (nonzero) digits is 15360, while the sum is 37.

The square root of 81681508 is about 9037.7822500877. The cubic root of 81681508 is about 433.8849461772.

The spelling of 81681508 in words is "eighty-one million, six hundred eighty-one thousand, five hundred eight".