20191909 has 4 divisors (see below), whose sum is σ = 20294604. Its totient is φ = 20089216.

The previous prime is 20191879. The next prime is 20191931. The reversal of 20191909 is 90919102.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 90919102 = 2 ⋅45459551.

It can be written as a sum of positive squares in 2 ways, for example, as 18301284 + 1890625 = 4278^2 + 1375^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20191909 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20191009) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 51052 + ... + 51445.

It is an arithmetic number, because the mean of its divisors is an integer number (5073651).

Almost surely, 2^20191909 is an apocalyptic number.

It is an amenable number.

20191909 is a deficient number, since it is larger than the sum of its proper divisors (102695).

20191909 is a wasteful number, since it uses less digits than its factorization.

20191909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 102694.

The product of its (nonzero) digits is 1458, while the sum is 31.

The square root of 20191909 is about 4493.5408087609. The cubic root of 20191909 is about 272.3072013899.

The spelling of 20191909 in words is "twenty million, one hundred ninety-one thousand, nine hundred nine".