81656181 has 10 divisors (see below), whose sum is σ = 121980342. Its totient is φ = 54437400.

The previous prime is 81656149. The next prime is 81656189. The reversal of 81656181 is 18165618.

81656181 is a `hidden beast` number, since 8 + 16 + 561 + 81 = 666.

It can be written as a sum of positive squares in only one way, i.e., 49914225 + 31741956 = 7065^2 + 5634^2 .

It is not a de Polignac number, because 81656181 - 2⁵ = 81656149 is a prime.

It is a super-3 number, since 3×81656181³ (a number of 25 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

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

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81656189) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 503970 + ... + 504131.

Almost surely, 2^81656181 is an apocalyptic number.

81656181 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

It is an amenable number.

81656181 is a deficient number, since it is larger than the sum of its proper divisors (40324161).

81656181 is a wasteful number, since it uses less digits than its factorization.

81656181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1008113 (or 1008104 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 81656181 is about 9036.3809680646. The cubic root of 81656181 is about 433.8400966134.

The spelling of 81656181 in words is "eighty-one million, six hundred fifty-six thousand, one hundred eighty-one".