81861639 has 16 divisors (see below), whose sum is σ = 111767040. Its totient is φ = 53271680.

The previous prime is 81861631. The next prime is 81861653. The reversal of 81861639 is 93616818.

It is not a de Polignac number, because 81861639 - 2³ = 81861631 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81861639.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81861631) 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 15 ways as a sum of consecutive naturals, for example, 92479 + ... + 93359.

It is an arithmetic number, because the mean of its divisors is an integer number (6985440).

Almost surely, 2^81861639 is an apocalyptic number.

81861639 is a deficient number, since it is larger than the sum of its proper divisors (29905401).

81861639 is a wasteful number, since it uses less digits than its factorization.

81861639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1590.

The product of its digits is 62208, while the sum is 42.

The square root of 81861639 is about 9047.7422045503. The cubic root of 81861639 is about 434.2036586547.

The spelling of 81861639 in words is "eighty-one million, eight hundred sixty-one thousand, six hundred thirty-nine".