91509015721 has 2 divisors, whose sum is σ = 91509015722. Its totient is φ = 91509015720.

The previous prime is 91509015683. The next prime is 91509015799. The reversal of 91509015721 is 12751090519.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 85383762025 + 6125253696 = 292205^2 + 78264^2 .

It is an emirp because it is prime and its reverse (12751090519) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91509015721 - 2¹⁵ = 91508982953 is a prime.

It is not a weakly prime, because it can be changed into another prime (91509010721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45754507860 + 45754507861.

It is an arithmetic number, because the mean of its divisors is an integer number (45754507861).

Almost surely, 2^91509015721 is an apocalyptic number.

It is an amenable number.

91509015721 is a deficient number, since it is larger than the sum of its proper divisors (1).

91509015721 is an equidigital number, since it uses as much as digits as its factorization.

91509015721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 28350, while the sum is 40.

The spelling of 91509015721 in words is "ninety-one billion, five hundred nine million, fifteen thousand, seven hundred twenty-one".