81387440 has 40 divisors (see below), whose sum is σ = 189705120. Its totient is φ = 32472576.

The previous prime is 81387437. The next prime is 81387443. The reversal of 81387440 is 4478318.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (81387437) and next prime (81387443).

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

It is a self number, because there is not a number n which added to its sum of digits gives 81387440.

It is not an unprimeable number, because it can be changed into a prime (81387443) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 37916 + ... + 40004.

It is an arithmetic number, because the mean of its divisors is an integer number (4742628).

Almost surely, 2^81387440 is an apocalyptic number.

81387440 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81387440 is an abundant number, since it is smaller than the sum of its proper divisors (108317680).

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

81387440 is a wasteful number, since it uses less digits than its factorization.

81387440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2589 (or 2583 counting only the distinct ones).

The product of its (nonzero) digits is 21504, while the sum is 35.

The square root of 81387440 is about 9021.4987668347. The cubic root of 81387440 is about 433.3636323324.

The spelling of 81387440 in words is "eighty-one million, three hundred eighty-seven thousand, four hundred forty".