81988613 has 6 divisors (see below), whose sum is σ = 95374566. Its totient is φ = 70275912.

The previous prime is 81988607. The next prime is 81988631. The reversal of 81988613 is 31688918.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 53611684 + 28376929 = 7322^2 + 5327^2 .

It is not a de Polignac number, because 81988613 - 2¹⁴ = 81972229 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81988693) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 836570 + ... + 836667.

It is an arithmetic number, because the mean of its divisors is an integer number (15895761).

Almost surely, 2^81988613 is an apocalyptic number.

It is an amenable number.

81988613 is a deficient number, since it is larger than the sum of its proper divisors (13385953).

81988613 is a wasteful number, since it uses less digits than its factorization.

81988613 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1673251 (or 1673244 counting only the distinct ones).

The product of its digits is 82944, while the sum is 44.

The square root of 81988613 is about 9054.7563744145. The cubic root of 81988613 is about 434.4280376416.

The spelling of 81988613 in words is "eighty-one million, nine hundred eighty-eight thousand, six hundred thirteen".