81102781 has 4 divisors (see below), whose sum is σ = 82213852. Its totient is φ = 79991712.

The previous prime is 81102751. The next prime is 81102817. The reversal of 81102781 is 18720118.

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 70644025 + 10458756 = 8405^2 + 3234^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81102781 is a prime.

It is a super-2 number, since 2×81102781² = 13155322171867922, 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 (81102701) 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, 555426 + ... + 555571.

It is an arithmetic number, because the mean of its divisors is an integer number (20553463).

Almost surely, 2^81102781 is an apocalyptic number.

It is an amenable number.

81102781 is a deficient number, since it is larger than the sum of its proper divisors (1111071).

81102781 is a wasteful number, since it uses less digits than its factorization.

81102781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1111070.

The product of its (nonzero) digits is 896, while the sum is 28.

The square root of 81102781 is about 9005.7082453297. The cubic root of 81102781 is about 432.8578009667.

Adding to 81102781 its reverse (18720118), we get a palindrome (99822899).

The spelling of 81102781 in words is "eighty-one million, one hundred two thousand, seven hundred eighty-one".