1661155516566 has 192 divisors, whose sum is σ = 4665625735680. Its totient is φ = 414805432320.

The previous prime is 1661155516481. The next prime is 1661155516567. The reversal of 1661155516566 is 6656155511661.

1661155516566 is a `hidden beast` number, since 1 + 6 + 6 + 1 + 15 + 55 + 16 + 566 = 666.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661155516567) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 56347206 + ... + 56376678.

It is an arithmetic number, because the mean of its divisors is an integer number (24300134040).

Almost surely, 2^{1661155516566} is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1661155516566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2332812867840).

1661155516566 is an abundant number, since it is smaller than the sum of its proper divisors (3004470219114).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1661155516566 is a wasteful number, since it uses less digits than its factorization.

1661155516566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31331 (or 31328 counting only the distinct ones).

The product of its digits is 4860000, while the sum is 54.

The spelling of 1661155516566 in words is "one trillion, six hundred sixty-one billion, one hundred fifty-five million, five hundred sixteen thousand, five hundred sixty-six".