1971809 has 6 divisors (see below), whose sum is σ = 2293794. Its totient is φ = 1690080.

The previous prime is 1971799. The next prime is 1971829. The reversal of 1971809 is 9081791.

It can be written as a sum of positive squares in only one way, i.e., 1254400 + 717409 = 1120^2 + 847^2 .

It is not a de Polignac number, because 1971809 - 2⁸ = 1971553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1971829) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 20072 + ... + 20169.

It is an arithmetic number, because the mean of its divisors is an integer number (382299).

2^1971809 is an apocalyptic number.

It is an amenable number.

1971809 is a deficient number, since it is larger than the sum of its proper divisors (321985).

1971809 is an equidigital number, since it uses as much as digits as its factorization.

1971809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40255 (or 40248 counting only the distinct ones).

The product of its (nonzero) digits is 4536, while the sum is 35.

The square root of 1971809 is about 1404.2111664561. The cubic root of 1971809 is about 125.3973277074.

The spelling of 1971809 in words is "one million, nine hundred seventy-one thousand, eight hundred nine".