81661755 has 16 divisors (see below), whose sum is σ = 149324544. Its totient is φ = 37331040.

The previous prime is 81661751. The next prime is 81661757. The reversal of 81661755 is 55716618.

It is not a de Polignac number, because 81661755 - 2² = 81661751 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81661751) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 388761 + ... + 388970.

It is an arithmetic number, because the mean of its divisors is an integer number (9332784).

Almost surely, 2^81661755 is an apocalyptic number.

81661755 is a deficient number, since it is larger than the sum of its proper divisors (67662789).

81661755 is a wasteful number, since it uses less digits than its factorization.

81661755 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 777746.

The product of its digits is 50400, while the sum is 39.

The square root of 81661755 is about 9036.6893827330. The cubic root of 81661755 is about 433.8499679611.

The spelling of 81661755 in words is "eighty-one million, six hundred sixty-one thousand, seven hundred fifty-five".