81644644618 has 16 divisors (see below), whose sum is σ = 130954782024. Its totient is φ = 38040601600.

The previous prime is 81644644591. The next prime is 81644644637.

It is a happy number.

81644644618 is nontrivially palindromic in base 10.

It can be written as a sum of positive squares in 4 ways, for example, as 66797953209 + 14846691409 = 258453^2 + 121847^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11884255 + ... + 11891122.

Almost surely, 2^81644644618 is an apocalyptic number.

81644644618 is a deficient number, since it is larger than the sum of its proper divisors (49310137406).

81644644618 is a wasteful number, since it uses less digits than its factorization.

81644644618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23775497.

The product of its digits is 3538944, while the sum is 52.

The spelling of 81644644618 in words is "eighty-one billion, six hundred forty-four million, six hundred forty-four thousand, six hundred eighteen".