661561775 has 48 divisors (see below), whose sum is σ = 986216640. Its totient is φ = 430617600.

The previous prime is 661561757. The next prime is 661561781. The reversal of 661561775 is 577165166.

It is not a de Polignac number, because 661561775 - 2¹² = 661557679 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 308507 + ... + 310643.

It is an arithmetic number, because the mean of its divisors is an integer number (20546180).

Almost surely, 2^661561775 is an apocalyptic number.

661561775 is a deficient number, since it is larger than the sum of its proper divisors (324654865).

661561775 is a wasteful number, since it uses less digits than its factorization.

661561775 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2244 (or 2239 counting only the distinct ones).

The product of its digits is 264600, while the sum is 44.

The square root of 661561775 is about 25720.8432015749. The cubic root of 661561775 is about 871.3449822242.

The spelling of 661561775 in words is "six hundred sixty-one million, five hundred sixty-one thousand, seven hundred seventy-five".