81281693 has 8 divisors (see below), whose sum is σ = 84188280. Its totient is φ = 78382080.

The previous prime is 81281687. The next prime is 81281713. The reversal of 81281693 is 39618218.

It can be written as a sum of positive squares in 4 ways, for example, as 44582329 + 36699364 = 6677^2 + 6058^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81281693 - 2¹² = 81277597 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 (81281623) 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, 36533 + ... + 38693.

It is an arithmetic number, because the mean of its divisors is an integer number (10523535).

Almost surely, 2^81281693 is an apocalyptic number.

It is an amenable number.

81281693 is a deficient number, since it is larger than the sum of its proper divisors (2906587).

81281693 is a wasteful number, since it uses less digits than its factorization.

81281693 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3487.

The product of its digits is 20736, while the sum is 38.

The square root of 81281693 is about 9015.6360285894. The cubic root of 81281693 is about 433.1758606646.

The spelling of 81281693 in words is "eighty-one million, two hundred eighty-one thousand, six hundred ninety-three".