81549981 has 6 divisors (see below), whose sum is σ = 117794430. Its totient is φ = 54366648.

The previous prime is 81549971. The next prime is 81549983. The reversal of 81549981 is 18994518.

81549981 is a `hidden beast` number, since 81 + 5 + 499 + 81 = 666.

It can be written as a sum of positive squares in only one way, i.e., 41024025 + 40525956 = 6405^2 + 6366^2 .

It is not a de Polignac number, because 81549981 - 2⁶ = 81549917 is a prime.

It is a super-2 number, since 2×81549981² = 13300798802200722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81549983) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4530546 + ... + 4530563.

It is an arithmetic number, because the mean of its divisors is an integer number (19632405).

Almost surely, 2^81549981 is an apocalyptic number.

It is an amenable number.

81549981 is a deficient number, since it is larger than the sum of its proper divisors (36244449).

81549981 is a wasteful number, since it uses less digits than its factorization.

81549981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9061115 (or 9061112 counting only the distinct ones).

The product of its digits is 103680, while the sum is 45.

The square root of 81549981 is about 9030.5028099215. The cubic root of 81549981 is about 433.6519344669.

The spelling of 81549981 in words is "eighty-one million, five hundred forty-nine thousand, nine hundred eighty-one".