661561509 has 16 divisors (see below), whose sum is σ = 1011935232. Its totient is φ = 376594608.

The previous prime is 661561507. The next prime is 661561541. The reversal of 661561509 is 905165166.

661561509 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 661561509 - 2¹ = 661561507 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661561501) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 54369 + ... + 65414.

It is an arithmetic number, because the mean of its divisors is an integer number (63245952).

Almost surely, 2^661561509 is an apocalyptic number.

It is an amenable number.

661561509 is a deficient number, since it is larger than the sum of its proper divisors (350373723).

661561509 is a wasteful number, since it uses less digits than its factorization.

661561509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 120056.

The product of its (nonzero) digits is 48600, while the sum is 39.

The square root of 661561509 is about 25720.8380306708. The cubic root of 661561509 is about 871.3448654411.

The spelling of 661561509 in words is "six hundred sixty-one million, five hundred sixty-one thousand, five hundred nine".