81561685 has 8 divisors (see below), whose sum is σ = 99956736. Its totient is φ = 63860880.

The previous prime is 81561679. The next prime is 81561691. The reversal of 81561685 is 58616518.

It is an interprime number because it is at equal distance from previous prime (81561679) and next prime (81561691).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81561685 - 2²³ = 73173077 is a prime.

It is a Duffinian number.

It is a congruent number.

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, 173301 + ... + 173770.

It is an arithmetic number, because the mean of its divisors is an integer number (12494592).

Almost surely, 2^81561685 is an apocalyptic number.

It is an amenable number.

81561685 is a deficient number, since it is larger than the sum of its proper divisors (18395051).

81561685 is a wasteful number, since it uses less digits than its factorization.

81561685 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 347123.

The product of its digits is 57600, while the sum is 40.

The square root of 81561685 is about 9031.1508126041. The cubic root of 81561685 is about 433.6726792887.

It can be divided in two parts, 815 and 61685, that added together give a square (62500 = 250²).

The spelling of 81561685 in words is "eighty-one million, five hundred sixty-one thousand, six hundred eighty-five".