81636381 has 12 divisors (see below), whose sum is σ = 119088060. Its totient is φ = 53884800.

The previous prime is 81636337. The next prime is 81636383. The reversal of 81636381 is 18363618.

81636381 is a `hidden beast` number, since 8 + 16 + 3 + 638 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 77264100 + 4372281 = 8790^2 + 2091^2 .

It is not a de Polignac number, because 81636381 - 2¹³ = 81628189 is a prime.

It is a super-2 number, since 2×81636381² = 13328997405554322, which contains 22 as substring.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81636383) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 43996 + ... + 45813.

It is an arithmetic number, because the mean of its divisors is an integer number (9924005).

Almost surely, 2^81636381 is an apocalyptic number.

It is an amenable number.

81636381 is a deficient number, since it is larger than the sum of its proper divisors (37451679).

81636381 is a wasteful number, since it uses less digits than its factorization.

81636381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 89916 (or 89913 counting only the distinct ones).

The product of its digits is 20736, while the sum is 36.

The square root of 81636381 is about 9035.2853303036. The cubic root of 81636381 is about 433.8050279135.

Adding to 81636381 its reverse (18363618), we get a palindrome (99999999).

The spelling of 81636381 in words is "eighty-one million, six hundred thirty-six thousand, three hundred eighty-one".