81781667 has 4 divisors (see below), whose sum is σ = 89216376. Its totient is φ = 74346960.

The previous prime is 81781639. The next prime is 81781697. The reversal of 81781667 is 76618718.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81781667 - 2¹⁴ = 81765283 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81781697) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3717338 + ... + 3717359.

It is an arithmetic number, because the mean of its divisors is an integer number (22304094).

Almost surely, 2^81781667 is an apocalyptic number.

81781667 is a deficient number, since it is larger than the sum of its proper divisors (7434709).

81781667 is a wasteful number, since it uses less digits than its factorization.

81781667 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7434708.

The product of its digits is 112896, while the sum is 44.

The square root of 81781667 is about 9043.3216795600. The cubic root of 81781667 is about 434.0622189886.

The spelling of 81781667 in words is "eighty-one million, seven hundred eighty-one thousand, six hundred sixty-seven".