81555565 has 16 divisors (see below), whose sum is σ = 120451968. Its totient is φ = 51621696.

The previous prime is 81555559. The next prime is 81555577. The reversal of 81555565 is 56555518.

It is a happy number.

It is not a de Polignac number, because 81555565 - 2³ = 81555557 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 89167 + ... + 90076.

It is an arithmetic number, because the mean of its divisors is an integer number (7528248).

Almost surely, 2^81555565 is an apocalyptic number.

It is an amenable number.

81555565 is a deficient number, since it is larger than the sum of its proper divisors (38896403).

81555565 is a wasteful number, since it uses less digits than its factorization.

81555565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179268.

The product of its digits is 150000, while the sum is 40.

The square root of 81555565 is about 9030.8119789972. The cubic root of 81555565 is about 433.6618321072.

The spelling of 81555565 in words is "eighty-one million, five hundred fifty-five thousand, five hundred sixty-five".