81555409 has 8 divisors (see below), whose sum is σ = 92995560. Its totient is φ = 70853376.

The previous prime is 81555407. The next prime is 81555427. The reversal of 81555409 is 90455518.

It can be written as a sum of positive squares in 4 ways, for example, as 13542400 + 68013009 = 3680^2 + 8247^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 81555409 - 2¹ = 81555407 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81555403) 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, 184294 + ... + 184735.

It is an arithmetic number, because the mean of its divisors is an integer number (11624445).

Almost surely, 2^81555409 is an apocalyptic number.

It is an amenable number.

81555409 is a deficient number, since it is larger than the sum of its proper divisors (11440151).

81555409 is a wasteful number, since it uses less digits than its factorization.

81555409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369059.

The product of its (nonzero) digits is 36000, while the sum is 37.

The square root of 81555409 is about 9030.8033418960. The cubic root of 81555409 is about 433.6615556034.

The spelling of 81555409 in words is "eighty-one million, five hundred fifty-five thousand, four hundred nine".