28121557 has 8 divisors (see below), whose sum is σ = 29647872. Its totient is φ = 26634000.

The previous prime is 28121521. The next prime is 28121581. The reversal of 28121557 is 75512182.

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 28121557 - 2¹⁵ = 28088789 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28121057) 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, 8194 + ... + 11107.

It is an arithmetic number, because the mean of its divisors is an integer number (3705984).

Almost surely, 2^28121557 is an apocalyptic number.

It is an amenable number.

28121557 is a deficient number, since it is larger than the sum of its proper divisors (1526315).

28121557 is a wasteful number, since it uses less digits than its factorization.

28121557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19379.

The product of its digits is 5600, while the sum is 31.

The square root of 28121557 is about 5302.9762398110. The cubic root of 28121557 is about 304.0976897780.

The spelling of 28121557 in words is "twenty-eight million, one hundred twenty-one thousand, five hundred fifty-seven".