1981209 has 4 divisors (see below), whose sum is σ = 2641616. Its totient is φ = 1320804.

The previous prime is 1981201. The next prime is 1981237. The reversal of 1981209 is 9021891.

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, and also an emirpimes, since its reverse is a distinct semiprime: 9021891 = 3 ⋅3007297.

It is not a de Polignac number, because 1981209 - 2³ = 1981201 is a prime.

It is a D-number.

It is a Duffinian number.

1981209 is a lucky number.

It is a plaindrome in base 11.

It is not an unprimeable number, because it can be changed into a prime (1981201) 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, 330199 + ... + 330204.

It is an arithmetic number, because the mean of its divisors is an integer number (660404).

2^1981209 is an apocalyptic number.

It is an amenable number.

1981209 is a deficient number, since it is larger than the sum of its proper divisors (660407).

1981209 is an equidigital number, since it uses as much as digits as its factorization.

1981209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 660406.

The product of its (nonzero) digits is 1296, while the sum is 30.

The square root of 1981209 is about 1407.5542618315. The cubic root of 1981209 is about 125.5962764458.

The spelling of 1981209 in words is "one million, nine hundred eighty-one thousand, two hundred nine".