1661209 has 6 divisors (see below), whose sum is σ = 1826090. Its totient is φ = 1510080.

The previous prime is 1661173. The next prime is 1661237. The reversal of 1661209 is 9021661.

It can be written as a sum of positive squares in only one way, i.e., 1334025 + 327184 = 1155^2 + 572^2 .

It is not a de Polignac number, because 1661209 - 2⁹ = 1660697 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661249) 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, 6744 + ... + 6985.

2^1661209 is an apocalyptic number.

It is an amenable number.

1661209 is a deficient number, since it is larger than the sum of its proper divisors (164881).

1661209 is a wasteful number, since it uses less digits than its factorization.

1661209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13751 (or 13740 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 25.

The square root of 1661209 is about 1288.8789702683. The cubic root of 1661209 is about 118.4335530439.

The spelling of 1661209 in words is "one million, six hundred sixty-one thousand, two hundred nine".