81555221 has 8 divisors (see below), whose sum is σ = 92037600. Its totient is φ = 71584240.

The previous prime is 81555197. The next prime is 81555233. The reversal of 81555221 is 12255518.

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 81555221 - 2⁶ = 81555157 is a prime.

It is a super-3 number, since 3×81555221³ (a number of 25 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (29).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81555121) 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, 127511 + ... + 128148.

It is an arithmetic number, because the mean of its divisors is an integer number (11504700).

Almost surely, 2^81555221 is an apocalyptic number.

It is an amenable number.

81555221 is a deficient number, since it is larger than the sum of its proper divisors (10482379).

81555221 is a wasteful number, since it uses less digits than its factorization.

81555221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 255699.

The product of its digits is 4000, while the sum is 29.

The square root of 81555221 is about 9030.7929330707. The cubic root of 81555221 is about 433.6612223803.

The spelling of 81555221 in words is "eighty-one million, five hundred fifty-five thousand, two hundred twenty-one".