81366399 has 6 divisors (see below), whose sum is σ = 117529256. Its totient is φ = 54244260.

The previous prime is 81366391. The next prime is 81366407. The reversal of 81366399 is 99366318.

81366399 is a `hidden beast` number, since 8 + 1 + 3 + 6 + 639 + 9 = 666.

It is an interprime number because it is at equal distance from previous prime (81366391) and next prime (81366407).

It is not a de Polignac number, because 81366399 - 2³ = 81366391 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 (81366391) 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 5 ways as a sum of consecutive naturals, for example, 4520347 + ... + 4520364.

Almost surely, 2^81366399 is an apocalyptic number.

81366399 is a deficient number, since it is larger than the sum of its proper divisors (36162857).

81366399 is a wasteful number, since it uses less digits than its factorization.

81366399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9040717 (or 9040714 counting only the distinct ones).

The product of its digits is 209952, while the sum is 45.

The square root of 81366399 is about 9020.3325326731. The cubic root of 81366399 is about 433.3262834488.

It can be divided in two parts, 8136 and 6399, that added together give a triangular number (14535 = T₁₇₀).

The spelling of 81366399 in words is "eighty-one million, three hundred sixty-six thousand, three hundred ninety-nine".