81561844 has 24 divisors (see below), whose sum is σ = 175672448. Its totient is φ = 32266080.

The previous prime is 81561829. The next prime is 81561863. The reversal of 81561844 is 44816518.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 111672 + ... + 112399.

Almost surely, 2^81561844 is an apocalyptic number.

It is an amenable number.

81561844 is an abundant number, since it is smaller than the sum of its proper divisors (94110604).

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

81561844 is a wasteful number, since it uses less digits than its factorization.

81561844 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 224095 (or 224093 counting only the distinct ones).

The product of its digits is 30720, while the sum is 37.

The square root of 81561844 is about 9031.1596154647. The cubic root of 81561844 is about 433.6729610955.

It can be divided in two parts, 8156 and 1844, that added together give a 4-th power (10000 = 10⁴).

The spelling of 81561844 in words is "eighty-one million, five hundred sixty-one thousand, eight hundred forty-four".