81131728 has 10 divisors (see below), whose sum is σ = 157192754. Its totient is φ = 40565856.

The previous prime is 81131719. The next prime is 81131731. The reversal of 81131728 is 82713118.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 80066704 + 1065024 = 8948^2 + 1032^2 .

It is a super-3 number, since 3×81131728³ (a number of 25 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81131728.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2535351 + ... + 2535382.

Almost surely, 2^81131728 is an apocalyptic number.

It is an amenable number.

81131728 is a deficient number, since it is larger than the sum of its proper divisors (76061026).

81131728 is a wasteful number, since it uses less digits than its factorization.

81131728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5070741 (or 5070735 counting only the distinct ones).

The product of its digits is 2688, while the sum is 31.

The square root of 81131728 is about 9007.3152492849. The cubic root of 81131728 is about 432.9092930125.

The spelling of 81131728 in words is "eighty-one million, one hundred thirty-one thousand, seven hundred twenty-eight".