81391699 has 4 divisors (see below), whose sum is σ = 86179464. Its totient is φ = 76603936.

The previous prime is 81391693. The next prime is 81391703. The reversal of 81391699 is 99619318.

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

It is a cyclic number.

It is not a de Polignac number, because 81391699 - 2¹⁹ = 80867411 is a prime.

It is a super-2 number, since 2×81391699² = 13249217332213202, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81391693) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2393857 + ... + 2393890.

It is an arithmetic number, because the mean of its divisors is an integer number (21544866).

Almost surely, 2^81391699 is an apocalyptic number.

81391699 is a deficient number, since it is larger than the sum of its proper divisors (4787765).

81391699 is a wasteful number, since it uses less digits than its factorization.

81391699 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4787764.

The product of its digits is 104976, while the sum is 46.

The square root of 81391699 is about 9021.7348109995. The cubic root of 81391699 is about 433.3711914985.

The spelling of 81391699 in words is "eighty-one million, three hundred ninety-one thousand, six hundred ninety-nine".