81783581 has 16 divisors (see below), whose sum is σ = 94348800. Its totient is φ = 70110000.

The previous prime is 81783571. The next prime is 81783587. The reversal of 81783581 is 18538718.

It is not a de Polignac number, because 81783581 - 2²⁶ = 14674717 is a prime.

It is a super-2 number, since 2×81783581² = 13377108242367122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81783587) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 51680 + ... + 53238.

It is an arithmetic number, because the mean of its divisors is an integer number (5896800).

Almost surely, 2^81783581 is an apocalyptic number.

It is an amenable number.

81783581 is a deficient number, since it is larger than the sum of its proper divisors (12565219).

81783581 is a wasteful number, since it uses less digits than its factorization.

81783581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1840.

The product of its digits is 53760, while the sum is 41.

The square root of 81783581 is about 9043.4275028885. The cubic root of 81783581 is about 434.0656051942.

The spelling of 81783581 in words is "eighty-one million, seven hundred eighty-three thousand, five hundred eighty-one".