81537444 has 36 divisors (see below), whose sum is σ = 213218460. Its totient is φ = 26241600.

The previous prime is 81537437. The next prime is 81537451. The reversal of 81537444 is 44473518.

81537444 is a `hidden beast` number, since 81 + 537 + 4 + 44 = 666.

It is an interprime number because it is at equal distance from previous prime (81537437) and next prime (81537451).

It can be written as a sum of positive squares in 2 ways, for example, as 57153600 + 24383844 = 7560^2 + 4938^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 81537399 and 81537408.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 38007 + ... + 40094.

It is an arithmetic number, because the mean of its divisors is an integer number (5922735).

Almost surely, 2^81537444 is an apocalyptic number.

It is an amenable number.

81537444 is an abundant number, since it is smaller than the sum of its proper divisors (131681016).

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

81537444 is a wasteful number, since it uses less digits than its factorization.

81537444 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78140 (or 78135 counting only the distinct ones).

The product of its digits is 53760, while the sum is 36.

The square root of 81537444 is about 9029.8086358461. The cubic root of 81537444 is about 433.6297109877.

The spelling of 81537444 in words is "eighty-one million, five hundred thirty-seven thousand, four hundred forty-four".