20155661665 has 4 divisors (see below), whose sum is σ = 24186794004. Its totient is φ = 16124529328.

The previous prime is 20155661641. The next prime is 20155661671. The reversal of 20155661665 is 56616655102.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3533232481 + 16622429184 = 59441^2 + 128928^2 .

It is a cyclic number.

It is not a de Polignac number, because 20155661665 - 2⁵ = 20155661633 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2015566162 + ... + 2015566171.

It is an arithmetic number, because the mean of its divisors is an integer number (6046698501).

Almost surely, 2^20155661665 is an apocalyptic number.

It is an amenable number.

20155661665 is a deficient number, since it is larger than the sum of its proper divisors (4031132339).

20155661665 is an equidigital number, since it uses as much as digits as its factorization.

20155661665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4031132338.

The product of its (nonzero) digits is 324000, while the sum is 43.

The spelling of 20155661665 in words is "twenty billion, one hundred fifty-five million, six hundred sixty-one thousand, six hundred sixty-five".