81660381 has 8 divisors (see below), whose sum is σ = 118778784. Its totient is φ = 49491120.

The previous prime is 81660379. The next prime is 81660389. The reversal of 81660381 is 18306618.

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

It is not a de Polignac number, because 81660381 - 2¹ = 81660379 is a prime.

It is a super-2 number, since 2×81660381² = 13336835650130322, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (33), and also a Moran number because the ratio is a prime number: 2474557 = 81660381 / (8 + 1 + 6 + 6 + 0 + 3 + 8 + 1).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81660389) 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, 1237246 + ... + 1237311.

It is an arithmetic number, because the mean of its divisors is an integer number (14847348).

Almost surely, 2^81660381 is an apocalyptic number.

It is an amenable number.

81660381 is a deficient number, since it is larger than the sum of its proper divisors (37118403).

81660381 is a wasteful number, since it uses less digits than its factorization.

81660381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2474571.

The product of its (nonzero) digits is 6912, while the sum is 33.

The square root of 81660381 is about 9036.6133589968. The cubic root of 81660381 is about 433.8475346997.

Adding to 81660381 its reverse (18306618), we get a palindrome (99966999).

The spelling of 81660381 in words is "eighty-one million, six hundred sixty thousand, three hundred eighty-one".