81405561 has 8 divisors (see below), whose sum is σ = 108622720. Its totient is φ = 54229392.

The previous prime is 81405529. The next prime is 81405563. The reversal of 81405561 is 16550418.

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

It is not a de Polignac number, because 81405561 - 2⁵ = 81405529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81405563) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5266 + ... + 13803.

It is an arithmetic number, because the mean of its divisors is an integer number (13577840).

Almost surely, 2^81405561 is an apocalyptic number.

It is an amenable number.

81405561 is a deficient number, since it is larger than the sum of its proper divisors (27217159).

81405561 is a wasteful number, since it uses less digits than its factorization.

81405561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20495.

The product of its (nonzero) digits is 4800, while the sum is 30.

The square root of 81405561 is about 9022.5030340810. The cubic root of 81405561 is about 433.3957929034.

Adding to 81405561 its reverse (16550418), we get a palindrome (97955979).

The spelling of 81405561 in words is "eighty-one million, four hundred five thousand, five hundred sixty-one".