81818181 has 40 divisors (see below), whose sum is σ = 126036504. Its totient is φ = 52876800.

The previous prime is 81818179. The next prime is 81818197. The reversal of 81818181 is 18181818.

It can be written as a sum of positive squares in 4 ways, for example, as 39125025 + 42693156 = 6255^2 + 6534^2 .

It is not a de Polignac number, because 81818181 - 2¹ = 81818179 is a prime.

It is a super-2 number, since 2×81818181² = 13388429484297522, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

81818181 is an undulating number in base 10.

81818181 is a modest number, since divided by 818181 gives 81 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81818111) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 597145 + ... + 597281.

Almost surely, 2^81818181 is an apocalyptic number.

81818181 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

It is an amenable number.

81818181 is a deficient number, since it is larger than the sum of its proper divisors (44218323).

81818181 is a wasteful number, since it uses less digits than its factorization.

81818181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 323 (or 314 counting only the distinct ones).

The product of its digits is 4096, while the sum is 36.

The square root of 81818181 is about 9045.3402921062. The cubic root of 81818181 is about 434.1268096245.

Adding to 81818181 its reverse (18181818), we get a palindrome (99999999).

The spelling of 81818181 in words is "eighty-one million, eight hundred eighteen thousand, one hundred eighty-one".