1991071509 has 16 divisors (see below), whose sum is σ = 3034675200. Its totient is φ = 1137507120.

The previous prime is 1991071493. The next prime is 1991071529. The reversal of 1991071509 is 9051701991.

It is a happy number.

It is not a de Polignac number, because 1991071509 - 2⁴ = 1991071493 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991071529) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 137392 + ... + 151190.

It is an arithmetic number, because the mean of its divisors is an integer number (189667200).

Almost surely, 2^1991071509 is an apocalyptic number.

It is an amenable number.

1991071509 is a deficient number, since it is larger than the sum of its proper divisors (1043603691).

1991071509 is a wasteful number, since it uses less digits than its factorization.

1991071509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20680.

The product of its (nonzero) digits is 25515, while the sum is 42.

The square root of 1991071509 is about 44621.4243273341. The cubic root of 1991071509 is about 1258.0433873755.

It can be divided in two parts, 19910 and 71509, that added together give a palindrome (91419).

The spelling of 1991071509 in words is "one billion, nine hundred ninety-one million, seventy-one thousand, five hundred nine".