11901666581 has 4 divisors (see below), whose sum is σ = 13601904672. Its totient is φ = 10201428492.

The previous prime is 11901666577. The next prime is 11901666587. The reversal of 11901666581 is 18566610911.

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, and also an emirpimes, since its reverse is a distinct semiprime: 18566610911 = 17 ⋅1092153583.

It is a cyclic number.

It is not a de Polignac number, because 11901666581 - 2² = 11901666577 is a prime.

It is a super-3 number, since 3×11901666581³ (a number of 31 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (11901666587) 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, 850119035 + ... + 850119048.

It is an arithmetic number, because the mean of its divisors is an integer number (3400476168).

Almost surely, 2^11901666581 is an apocalyptic number.

It is an amenable number.

11901666581 is a deficient number, since it is larger than the sum of its proper divisors (1700238091).

11901666581 is an equidigital number, since it uses as much as digits as its factorization.

11901666581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1700238090.

The product of its (nonzero) digits is 77760, while the sum is 44.

The spelling of 11901666581 in words is "eleven billion, nine hundred one million, six hundred sixty-six thousand, five hundred eighty-one".