81785281 has 4 divisors (see below), whose sum is σ = 83995732. Its totient is φ = 79574832.

The previous prime is 81785273. The next prime is 81785339. The reversal of 81785281 is 18258718.

81785281 = T₁₁₅₈ + T₁₁₅₉ + ... + T₁₂₆₈.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 68890000 + 12895281 = 8300^2 + 3591^2 .

It is a cyclic number.

It is not a de Polignac number, because 81785281 - 2³ = 81785273 is a prime.

It is a super-3 number, since 3×81785281³ (a number of 25 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81785251) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1105170 + ... + 1105243.

It is an arithmetic number, because the mean of its divisors is an integer number (20998933).

Almost surely, 2^81785281 is an apocalyptic number.

It is an amenable number.

81785281 is a deficient number, since it is larger than the sum of its proper divisors (2210451).

81785281 is a wasteful number, since it uses less digits than its factorization.

81785281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2210450.

The product of its digits is 35840, while the sum is 40.

The square root of 81785281 is about 9043.5214933122. The cubic root of 81785281 is about 434.0686127515.

The spelling of 81785281 in words is "eighty-one million, seven hundred eighty-five thousand, two hundred eighty-one".