661509 has 12 divisors (see below), whose sum is σ = 986752. Its totient is φ = 426600.

The previous prime is 661483. The next prime is 661513. The reversal of 661509 is 905166.

It is not a de Polignac number, because 661509 - 2⁵ = 661477 is a prime.

It is a Duffinian number.

661509 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661009) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 907 + ... + 1464.

2⁶⁶¹⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

661509 is a deficient number, since it is larger than the sum of its proper divisors (325243).

661509 is a wasteful number, since it uses less digits than its factorization.

661509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2408 (or 2405 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 27.

The square root of 661509 is about 813.3320355181. The cubic root of 661509 is about 87.1321811572.

The spelling of 661509 in words is "six hundred sixty-one thousand, five hundred nine".