81391057 has 8 divisors (see below), whose sum is σ = 88889472. Its totient is φ = 73909200.

The previous prime is 81391049. The next prime is 81391067. The reversal of 81391057 is 75019318.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81391057 - 2³ = 81391049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81391067) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7608 + ... + 14854.

It is an arithmetic number, because the mean of its divisors is an integer number (11111184).

Almost surely, 2^81391057 is an apocalyptic number.

It is an amenable number.

81391057 is a deficient number, since it is larger than the sum of its proper divisors (7498415).

81391057 is a wasteful number, since it uses less digits than its factorization.

81391057 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8279.

The product of its (nonzero) digits is 7560, while the sum is 34.

The square root of 81391057 is about 9021.6992301894. The cubic root of 81391057 is about 433.3700520496.

The spelling of 81391057 in words is "eighty-one million, three hundred ninety-one thousand, fifty-seven".