1661561667 has 40 divisors (see below), whose sum is σ = 2575964160. Its totient is φ = 1066549680.

The previous prime is 1661561639. The next prime is 1661561683. The reversal of 1661561667 is 7661651661.

1661561667 is a `hidden beast` number, since 16 + 6 + 15 + 616 + 6 + 7 = 666.

It is not a de Polignac number, because 1661561667 - 2⁸ = 1661561411 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1661511667) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 243934 + ... + 250652.

It is an arithmetic number, because the mean of its divisors is an integer number (64399104).

Almost surely, 2^1661561667 is an apocalyptic number.

1661561667 is a deficient number, since it is larger than the sum of its proper divisors (914402493).

1661561667 is an equidigital number, since it uses as much as digits as its factorization.

1661561667 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6845 (or 6836 counting only the distinct ones).

The product of its digits is 272160, while the sum is 45.

The square root of 1661561667 is about 40762.2578741659. The cubic root of 1661561667 is about 1184.4193341633.

The spelling of 1661561667 in words is "one billion, six hundred sixty-one million, five hundred sixty-one thousand, six hundred sixty-seven".