28720081 has 8 divisors (see below), whose sum is σ = 31437224. Its totient is φ = 26075520.

The previous prime is 28720073. The next prime is 28720091. The reversal of 28720081 is 18002782.

It can be written as a sum of positive squares in 4 ways, for example, as 2873025 + 25847056 = 1695^2 + 5084^2 .

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 28720081 - 2³ = 28720073 is a prime.

It is a super-2 number, since 2×28720081² = 1649686105293122, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (28720091) 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, 17316 + ... + 18901.

It is an arithmetic number, because the mean of its divisors is an integer number (3929653).

Almost surely, 2^28720081 is an apocalyptic number.

It is an amenable number.

28720081 is a deficient number, since it is larger than the sum of its proper divisors (2717143).

28720081 is a wasteful number, since it uses less digits than its factorization.

28720081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36291.

The product of its (nonzero) digits is 1792, while the sum is 28.

The square root of 28720081 is about 5359.1119600173. Note that the first 3 decimals coincide. The cubic root of 28720081 is about 306.2399793473.

The spelling of 28720081 in words is "twenty-eight million, seven hundred twenty thousand, eighty-one".