991721488625801 has 12 divisors (see below), whose sum is σ = 1019537032339980. Its totient is φ = 964645701647040.

The previous prime is 991721488625789. The next prime is 991721488625893. The reversal of 991721488625801 is 108526884127199.

991721488625801 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 6 ways, for example, as 100744360048201 + 890977128577600 = 10037149^2 + 29849240^2 .

It is not a de Polignac number, because 991721488625801 - 2¹⁴ = 991721488609417 is a prime.

It is a super-2 number, since 2×991721488625801² (a number of 31 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991721488622801) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 97441706 + ... + 107136963.

It is an arithmetic number, because the mean of its divisors is an integer number (84961419361665).

Almost surely, 2^{991721488625801} is an apocalyptic number.

It is an amenable number.

991721488625801 is a deficient number, since it is larger than the sum of its proper divisors (27815543714179).

991721488625801 is a wasteful number, since it uses less digits than its factorization.

991721488625801 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 204582284 (or 204582247 counting only the distinct ones).

The product of its (nonzero) digits is 139345920, while the sum is 71.

The spelling of 991721488625801 in words is "nine hundred ninety-one trillion, seven hundred twenty-one billion, four hundred eighty-eight million, six hundred twenty-five thousand, eight hundred one".