1561611666 has 16 divisors (see below), whose sum is σ = 3125265984. Its totient is φ = 520196784.

The previous prime is 1561611659. The next prime is 1561611719. The reversal of 1561611666 is 6661161651.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 75081 + ... + 93596.

It is an arithmetic number, because the mean of its divisors is an integer number (195329124).

Almost surely, 2^1561611666 is an apocalyptic number.

1561611666 is an abundant number, since it is smaller than the sum of its proper divisors (1563654318).

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

1561611666 is a wasteful number, since it uses less digits than its factorization.

1561611666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 170225.

The product of its digits is 38880, while the sum is 39.

The square root of 1561611666 is about 39517.2325194971. The cubic root of 1561611666 is about 1160.1772583856.

The spelling of 1561611666 in words is "one billion, five hundred sixty-one million, six hundred eleven thousand, six hundred sixty-six".