28721381 has 16 divisors (see below), whose sum is σ = 32986800. Its totient is φ = 24920064.

The previous prime is 28721353. The next prime is 28721383. The reversal of 28721381 is 18312782.

It can be written as a sum of positive squares in 8 ways, for example, as 17222500 + 11498881 = 4150^2 + 3391^2 .

It is not a de Polignac number, because 28721381 - 2⁶ = 28721317 is a prime.

It is a super-2 number, since 2×28721381² = 1649835453094322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28721383) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 36965 + ... + 37733.

It is an arithmetic number, because the mean of its divisors is an integer number (2061675).

Almost surely, 2^28721381 is an apocalyptic number.

It is an amenable number.

28721381 is a deficient number, since it is larger than the sum of its proper divisors (4265419).

28721381 is an equidigital number, since it uses as much as digits as its factorization.

28721381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 825 (or 799 counting only the distinct ones).

The product of its digits is 5376, while the sum is 32.

The square root of 28721381 is about 5359.2332473965. The cubic root of 28721381 is about 306.2445998770.

The spelling of 28721381 in words is "twenty-eight million, seven hundred twenty-one thousand, three hundred eighty-one".