3991609 has 2 divisors, whose sum is σ = 3991610. Its totient is φ = 3991608.

The previous prime is 3991607. The next prime is 3991613. The reversal of 3991609 is 9061993.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 3988009 + 3600 = 1997^2 + 60^2 .

It is a cyclic number.

It is not a de Polignac number, because 3991609 - 2¹ = 3991607 is a prime.

Together with 3991607, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (3991601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1995804 + 1995805.

It is an arithmetic number, because the mean of its divisors is an integer number (1995805).

Almost surely, 2^3991609 is an apocalyptic number.

It is an amenable number.

3991609 is a deficient number, since it is larger than the sum of its proper divisors (1).

3991609 is an equidigital number, since it uses as much as digits as its factorization.

3991609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13122, while the sum is 37.

The square root of 3991609 is about 1997.9011487058. The cubic root of 3991609 is about 158.6290284716.

The spelling of 3991609 in words is "three million, nine hundred ninety-one thousand, six hundred nine".