91721517 has 4 divisors (see below), whose sum is σ = 122295360. Its totient is φ = 61147676.

The previous prime is 91721471. The next prime is 91721521. The reversal of 91721517 is 71512719.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 71512719 = 3 ⋅23837573.

It is a cyclic number.

It is not a de Polignac number, because 91721517 - 2¹⁸ = 91459373 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91721527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15286917 + ... + 15286922.

It is an arithmetic number, because the mean of its divisors is an integer number (30573840).

Almost surely, 2^91721517 is an apocalyptic number.

It is an amenable number.

91721517 is a deficient number, since it is larger than the sum of its proper divisors (30573843).

91721517 is a wasteful number, since it uses less digits than its factorization.

91721517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30573842.

The product of its digits is 4410, while the sum is 33.

The square root of 91721517 is about 9577.1351144275. The cubic root of 91721517 is about 450.9797861485.

The spelling of 91721517 in words is "ninety-one million, seven hundred twenty-one thousand, five hundred seventeen".