81399440 has 40 divisors (see below), whose sum is σ = 189680568. Its totient is φ = 32486400.

The previous prime is 81399431. The next prime is 81399449. The reversal of 81399440 is 4499318.

It is an interprime number because it is at equal distance from previous prime (81399431) and next prime (81399449).

It can be written as a sum of positive squares in 4 ways, for example, as 15335056 + 66064384 = 3916^2 + 8128^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is a junction number, because it is equal to n+sod(n) for n = 81399394 and 81399403.

It is not an unprimeable number, because it can be changed into a prime (81399449) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 47234 + ... + 48926.

Almost surely, 2^81399440 is an apocalyptic number.

81399440 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81399440 is an abundant number, since it is smaller than the sum of its proper divisors (108281128).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81399440 is a wasteful number, since it uses less digits than its factorization.

81399440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2307 (or 2301 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 38.

The square root of 81399440 is about 9022.1638202817. The cubic root of 81399440 is about 433.3849300823.

The spelling of 81399440 in words is "eighty-one million, three hundred ninety-nine thousand, four hundred forty".