1661155809 has 16 divisors (see below), whose sum is σ = 2242265088. Its totient is φ = 1093820112.

The previous prime is 1661155789. The next prime is 1661155813. The reversal of 1661155809 is 9085511661.

It is not a de Polignac number, because 1661155809 - 2²⁵ = 1627601377 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1661155829) 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, 76884 + ... + 96090.

It is an arithmetic number, because the mean of its divisors is an integer number (140141568).

Almost surely, 2^1661155809 is an apocalyptic number.

It is an amenable number.

1661155809 is a deficient number, since it is larger than the sum of its proper divisors (581109279).

1661155809 is a wasteful number, since it uses less digits than its factorization.

1661155809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19564.

The product of its (nonzero) digits is 64800, while the sum is 42.

The square root of 1661155809 is about 40757.2792148838. The cubic root of 1661155809 is about 1184.3228897126.

The spelling of 1661155809 in words is "one billion, six hundred sixty-one million, one hundred fifty-five thousand, eight hundred nine".