1009999991 has 16 divisors (see below), whose sum is σ = 1356085248. Its totient is φ = 726472800.

The previous prime is 1009999979. The next prime is 1009999999. The reversal of 1009999991 is 1999999001.

It is a cyclic number.

It is not a de Polignac number, because 1009999991 - 2²⁶ = 942891127 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1009999999) 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, 503495 + ... + 505496.

It is an arithmetic number, because the mean of its divisors is an integer number (84755328).

Almost surely, 2^1009999991 is an apocalyptic number.

1009999991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

1009999991 is a deficient number, since it is larger than the sum of its proper divisors (346085257).

1009999991 is a wasteful number, since it uses less digits than its factorization.

1009999991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1009022.

The product of its (nonzero) digits is 531441, while the sum is 56.

The square root of 1009999991 is about 31780.4970225451. The cubic root of 1009999991 is about 1003.3222805619.

The spelling of 1009999991 in words is "one billion, nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".