1665777961 has 4 divisors (see below), whose sum is σ = 1667549124. Its totient is φ = 1664006800.

The previous prime is 1665777959. The next prime is 1665777977. The reversal of 1665777961 is 1697775661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1697775661 = 397 ⋅4276513.

It can be written as a sum of positive squares in 2 ways, for example, as 391287961 + 1274490000 = 19781^2 + 35700^2 .

It is a cyclic number.

It is not a de Polignac number, because 1665777961 - 2¹ = 1665777959 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1645777961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 884170 + ... + 886051.

It is an arithmetic number, because the mean of its divisors is an integer number (416887281).

Almost surely, 2^1665777961 is an apocalyptic number.

It is an amenable number.

1665777961 is a deficient number, since it is larger than the sum of its proper divisors (1771163).

1665777961 is an equidigital number, since it uses as much as digits as its factorization.

1665777961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1771162.

The product of its digits is 3333960, while the sum is 55.

The square root of 1665777961 is about 40813.9432179739. The cubic root of 1665777961 is about 1185.4203286135.

The spelling of 1665777961 in words is "one billion, six hundred sixty-five million, seven hundred seventy-seven thousand, nine hundred sixty-one".