81555531 has 4 divisors (see below), whose sum is σ = 108740712. Its totient is φ = 54370352.

The previous prime is 81555517. The next prime is 81555533. The reversal of 81555531 is 13555518.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81555531 - 2⁷ = 81555403 is a prime.

It is a super-2 number, since 2×81555531² = 13302609273383922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81555492 and 81555501.

It is not an unprimeable number, because it can be changed into a prime (81555533) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13592586 + ... + 13592591.

It is an arithmetic number, because the mean of its divisors is an integer number (27185178).

Almost surely, 2^81555531 is an apocalyptic number.

81555531 is a deficient number, since it is larger than the sum of its proper divisors (27185181).

81555531 is a wasteful number, since it uses less digits than its factorization.

81555531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27185180.

The product of its digits is 15000, while the sum is 33.

The square root of 81555531 is about 9030.8100965528. The cubic root of 81555531 is about 433.6617718436.

The spelling of 81555531 in words is "eighty-one million, five hundred fifty-five thousand, five hundred thirty-one".