1661655565 has 32 divisors (see below), whose sum is σ = 2150071776. Its totient is φ = 1228308480.

The previous prime is 1661655559. The next prime is 1661655571. The reversal of 1661655565 is 5655561661.

It is an interprime number because it is at equal distance from previous prime (1661655559) and next prime (1661655571).

It can be written as a sum of positive squares in 16 ways, for example, as 89453764 + 1572201801 = 9458^2 + 39651^2 .

It is not a de Polignac number, because 1661655565 - 2¹³ = 1661647373 is a prime.

It is a super-2 number, since 2×1661655565² = 5522198433390938450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1743129 + ... + 1744081.

It is an arithmetic number, because the mean of its divisors is an integer number (67189743).

Almost surely, 2^1661655565 is an apocalyptic number.

It is an amenable number.

1661655565 is a deficient number, since it is larger than the sum of its proper divisors (488416211).

1661655565 is a wasteful number, since it uses less digits than its factorization.

1661655565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1329.

The product of its digits is 810000, while the sum is 46.

The square root of 1661655565 is about 40763.4096341314. The cubic root of 1661655565 is about 1184.4416450038.

The spelling of 1661655565 in words is "one billion, six hundred sixty-one million, six hundred fifty-five thousand, five hundred sixty-five".