91771308721 has 4 divisors (see below), whose sum is σ = 91791738612. Its totient is φ = 91750878832.

The previous prime is 91771308697. The next prime is 91771308751. The reversal of 91771308721 is 12780317719.

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

It can be written as a sum of positive squares in 2 ways, for example, as 61273576225 + 30497732496 = 247535^2 + 174636^2 .

It is a cyclic number.

It is not a de Polignac number, because 91771308721 - 2⁵ = 91771308689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (91771308751) 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, 10208206 + ... + 10217191.

It is an arithmetic number, because the mean of its divisors is an integer number (22947934653).

Almost surely, 2^91771308721 is an apocalyptic number.

It is an amenable number.

91771308721 is a deficient number, since it is larger than the sum of its proper divisors (20429891).

91771308721 is a wasteful number, since it uses less digits than its factorization.

91771308721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20429890.

The product of its (nonzero) digits is 148176, while the sum is 46.

The spelling of 91771308721 in words is "ninety-one billion, seven hundred seventy-one million, three hundred eight thousand, seven hundred twenty-one".