661811643 has 12 divisors (see below), whose sum is σ = 956178288. Its totient is φ = 441102480.

The previous prime is 661811641. The next prime is 661811651. The reversal of 661811643 is 346118166.

661811643 is a `hidden beast` number, since 6 + 6 + 1 + 8 + 1 + 1 + 643 = 666.

It is not a de Polignac number, because 661811643 - 2¹ = 661811641 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 661811598 and 661811607.

It is not an unprimeable number, because it can be changed into a prime (661811641) 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, 56938 + ... + 67568.

It is an arithmetic number, because the mean of its divisors is an integer number (79681524).

Almost surely, 2^661811643 is an apocalyptic number.

661811643 is a deficient number, since it is larger than the sum of its proper divisors (294366645).

661811643 is a wasteful number, since it uses less digits than its factorization.

661811643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17554 (or 17551 counting only the distinct ones).

The product of its digits is 20736, while the sum is 36.

The square root of 661811643 is about 25725.7000487839. The cubic root of 661811643 is about 871.4546690448.

The spelling of 661811643 in words is "six hundred sixty-one million, eight hundred eleven thousand, six hundred forty-three".