81688257 has 20 divisors (see below), whose sum is σ = 139461696. Its totient is φ = 46678680.

The previous prime is 81688253. The next prime is 81688297. The reversal of 81688257 is 75288618.

It is not a de Polignac number, because 81688257 - 2² = 81688253 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81688253) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 71469 + ... + 72602.

Almost surely, 2^81688257 is an apocalyptic number.

It is an amenable number.

81688257 is a deficient number, since it is larger than the sum of its proper divisors (57773439).

81688257 is a wasteful number, since it uses less digits than its factorization.

81688257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 144090 (or 144081 counting only the distinct ones).

The product of its digits is 215040, while the sum is 45.

The square root of 81688257 is about 9038.1556193728. The cubic root of 81688257 is about 433.8968958784.

The spelling of 81688257 in words is "eighty-one million, six hundred eighty-eight thousand, two hundred fifty-seven".