81939618 has 12 divisors (see below), whose sum is σ = 177535878. Its totient is φ = 27313200.

The previous prime is 81939617. The next prime is 81939619. The reversal of 81939618 is 81693918.

It is an interprime number because it is at equal distance from previous prime (81939617) and next prime (81939619).

It can be written as a sum of positive squares in only one way, i.e., 65561409 + 16378209 = 8097^2 + 4047^2 .

It is not an unprimeable number, because it can be changed into a prime (81939617) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2276083 + ... + 2276118.

Almost surely, 2^81939618 is an apocalyptic number.

81939618 is an abundant number, since it is smaller than the sum of its proper divisors (95596260).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81939618 is a wasteful number, since it uses less digits than its factorization.

81939618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4552209 (or 4552206 counting only the distinct ones).

The product of its digits is 93312, while the sum is 45.

The square root of 81939618 is about 9052.0504859396. The cubic root of 81939618 is about 434.3414847975.

The spelling of 81939618 in words is "eighty-one million, nine hundred thirty-nine thousand, six hundred eighteen".