81660281 has 4 divisors (see below), whose sum is σ = 85210752. Its totient is φ = 78109812.

The previous prime is 81660263. The next prime is 81660283. The reversal of 81660281 is 18206618.

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: 18206618 = 2 ⋅9103309.

It is a cyclic number.

It is not a de Polignac number, because 81660281 - 2¹⁴ = 81643897 is a prime.

It is a super-2 number, since 2×81660281² = 13336802985997922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81660283) 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, 1775201 + ... + 1775246.

It is an arithmetic number, because the mean of its divisors is an integer number (21302688).

Almost surely, 2^81660281 is an apocalyptic number.

It is an amenable number.

81660281 is a deficient number, since it is larger than the sum of its proper divisors (3550471).

81660281 is a wasteful number, since it uses less digits than its factorization.

81660281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3550470.

The product of its (nonzero) digits is 4608, while the sum is 32.

The square root of 81660281 is about 9036.6078259488. The cubic root of 81660281 is about 433.8473576054.

Adding to 81660281 its reverse (18206618), we get a palindrome (99866899).

The spelling of 81660281 in words is "eighty-one million, six hundred sixty thousand, two hundred eighty-one".