91721009 has 4 divisors (see below), whose sum is σ = 91814004. Its totient is φ = 91628016.

The previous prime is 91720991. The next prime is 91721011. The reversal of 91721009 is 90012719.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 90012719 = 5653 ⋅15923.

It can be written as a sum of positive squares in 2 ways, for example, as 68227600 + 23493409 = 8260^2 + 4847^2 .

It is a cyclic number.

It is not a de Polignac number, because 91721009 - 2²⁰ = 90672433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (91721909) 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, 45002 + ... + 46995.

It is an arithmetic number, because the mean of its divisors is an integer number (22953501).

Almost surely, 2^91721009 is an apocalyptic number.

It is an amenable number.

91721009 is a deficient number, since it is larger than the sum of its proper divisors (92995).

91721009 is an equidigital number, since it uses as much as digits as its factorization.

91721009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92994.

The product of its (nonzero) digits is 1134, while the sum is 29.

The square root of 91721009 is about 9577.1085928896. The cubic root of 91721009 is about 450.9789535625.

The spelling of 91721009 in words is "ninety-one million, seven hundred twenty-one thousand, nine".