81978391 has 8 divisors (see below), whose sum is σ = 89510400. Its totient is φ = 74459640.

The previous prime is 81978349. The next prime is 81978401. The reversal of 81978391 is 19387918.

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 81978391 - 2⁷ = 81978263 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81958391) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13240 + ... + 18418.

It is an arithmetic number, because the mean of its divisors is an integer number (11188800).

Almost surely, 2^81978391 is an apocalyptic number.

81978391 is a deficient number, since it is larger than the sum of its proper divisors (7532009).

81978391 is a wasteful number, since it uses less digits than its factorization.

81978391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6629.

The product of its digits is 108864, while the sum is 46.

The square root of 81978391 is about 9054.1919020971. The cubic root of 81978391 is about 434.4099826630.

It can be divided in two parts, 81978 and 391, that added together give a square (82369 = 287²).

The spelling of 81978391 in words is "eighty-one million, nine hundred seventy-eight thousand, three hundred ninety-one".