1661665261 has 8 divisors (see below), whose sum is σ = 1704515904. Its totient is φ = 1618925280.

The previous prime is 1661665259. The next prime is 1661665267. The reversal of 1661665261 is 1625661661.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1661665261 - 2¹ = 1661665259 is a prime.

It is a super-2 number, since 2×1661665261² = 5522262879228396242, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661665267) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3190 + ... + 57736.

It is an arithmetic number, because the mean of its divisors is an integer number (213064488).

Almost surely, 2^1661665261 is an apocalyptic number.

It is an amenable number.

1661665261 is a deficient number, since it is larger than the sum of its proper divisors (42850643).

1661665261 is an equidigital number, since it uses as much as digits as its factorization.

1661665261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55331.

The product of its digits is 77760, while the sum is 40.

The square root of 1661665261 is about 40763.5285641467. The cubic root of 1661665261 is about 1184.4439487952.

The spelling of 1661665261 in words is "one billion, six hundred sixty-one million, six hundred sixty-five thousand, two hundred sixty-one".