661609 has 4 divisors (see below), whose sum is σ = 712516. Its totient is φ = 610704.

The previous prime is 661607. The next prime is 661613. The reversal of 661609 is 906166.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 29584 + 632025 = 172^2 + 795^2 .

It is a cyclic number.

It is not a de Polignac number, because 661609 - 2¹ = 661607 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661603) 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, 25434 + ... + 25459.

It is an arithmetic number, because the mean of its divisors is an integer number (178129).

2⁶⁶¹⁶⁰⁹ is an apocalyptic number.

It is an amenable number.

661609 is a deficient number, since it is larger than the sum of its proper divisors (50907).

661609 is a wasteful number, since it uses less digits than its factorization.

661609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50906.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 661609 is about 813.3935087029. The cubic root of 661609 is about 87.1365715127.

The spelling of 661609 in words is "six hundred sixty-one thousand, six hundred nine".