1991544486581 has 8 divisors (see below), whose sum is σ = 2144798023704. Its totient is φ = 1838299207680.

The previous prime is 1991544486559. The next prime is 1991544486671. The reversal of 1991544486581 is 1856844451991.

It can be written as a sum of positive squares in 4 ways, for example, as 29278632100 + 1962265854481 = 171110^2 + 1400809^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 1991544486581 - 2²² = 1991540292277 is a prime.

It is a super-2 number, since 2×1991544486581² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991544486521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1559096 + ... + 2532561.

It is an arithmetic number, because the mean of its divisors is an integer number (268099752963).

Almost surely, 2^{1991544486581} is an apocalyptic number.

It is an amenable number.

1991544486581 is a deficient number, since it is larger than the sum of its proper divisors (153253537123).

1991544486581 is a wasteful number, since it uses less digits than its factorization.

1991544486581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4129111.

The product of its digits is 49766400, while the sum is 65.

The spelling of 1991544486581 in words is "one trillion, nine hundred ninety-one billion, five hundred forty-four million, four hundred eighty-six thousand, five hundred eighty-one".