1981909 has 4 divisors (see below), whose sum is σ = 2086240. Its totient is φ = 1877580.

The previous prime is 1981901. The next prime is 1981919. The reversal of 1981909 is 9091891.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 1981909 - 2³ = 1981901 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 (1981901) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 52137 + ... + 52174.

It is an arithmetic number, because the mean of its divisors is an integer number (521560).

2^1981909 is an apocalyptic number.

1981909 is a gapful number since it is divisible by the number (19) formed by its first and last digit.

It is an amenable number.

1981909 is a deficient number, since it is larger than the sum of its proper divisors (104331).

1981909 is a wasteful number, since it uses less digits than its factorization.

1981909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104330.

The product of its (nonzero) digits is 5832, while the sum is 37.

The square root of 1981909 is about 1407.8028981360. The cubic root of 1981909 is about 125.6110665800.

The spelling of 1981909 in words is "one million, nine hundred eighty-one thousand, nine hundred nine".