1665551661 has 4 divisors (see below), whose sum is σ = 2220735552. Its totient is φ = 1110367772.

The previous prime is 1665551653. The next prime is 1665551687. The reversal of 1665551661 is 1661555661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1665551661 - 2³ = 1665551653 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1665551611) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 277591941 + ... + 277591946.

It is an arithmetic number, because the mean of its divisors is an integer number (555183888).

Almost surely, 2^1665551661 is an apocalyptic number.

It is an amenable number.

1665551661 is a deficient number, since it is larger than the sum of its proper divisors (555183891).

1665551661 is an equidigital number, since it uses as much as digits as its factorization.

1665551661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 555183890.

The product of its digits is 162000, while the sum is 42.

The square root of 1665551661 is about 40811.1707869304. The cubic root of 1665551661 is about 1185.3666454346.

The spelling of 1665551661 in words is "one billion, six hundred sixty-five million, five hundred fifty-one thousand, six hundred sixty-one".