81338781 has 4 divisors (see below), whose sum is σ = 108451712. Its totient is φ = 54225852.

The previous prime is 81338779. The next prime is 81338783. The reversal of 81338781 is 18783318.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (81338779) and next prime (81338783).

It is not a de Polignac number, because 81338781 - 2¹ = 81338779 is a prime.

It is a super-2 number, since 2×81338781² = 13231994589131922, 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 (81338783) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13556461 + ... + 13556466.

It is an arithmetic number, because the mean of its divisors is an integer number (27112928).

Almost surely, 2^81338781 is an apocalyptic number.

It is an amenable number.

81338781 is a deficient number, since it is larger than the sum of its proper divisors (27112931).

81338781 is a wasteful number, since it uses less digits than its factorization.

81338781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27112930.

The product of its digits is 32256, while the sum is 39.

The square root of 81338781 is about 9018.8015279193. The cubic root of 81338781 is about 433.2772502698.

The spelling of 81338781 in words is "eighty-one million, three hundred thirty-eight thousand, seven hundred eighty-one".