28721628 has 72 divisors (see below), whose sum is σ = 81118128. Its totient is φ = 8833536.

The previous prime is 28721617. The next prime is 28721647. The reversal of 28721628 is 82612782.

It is a happy number.

28721628 is a `hidden beast` number, since 2 + 8 + 7 + 21 + 628 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 28721592 and 28721601.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 11500 + ... + 13772.

Almost surely, 2^28721628 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 28721628, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40559064).

28721628 is an abundant number, since it is smaller than the sum of its proper divisors (52396500).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

28721628 is a wasteful number, since it uses less digits than its factorization.

28721628 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2305 (or 2291 counting only the distinct ones).

The product of its digits is 21504, while the sum is 36.

The square root of 28721628 is about 5359.2562916882. The cubic root of 28721628 is about 306.2454777619.

The spelling of 28721628 in words is "twenty-eight million, seven hundred twenty-one thousand, six hundred twenty-eight".