28137721 has 2 divisors, whose sum is σ = 28137722. Its totient is φ = 28137720.

The previous prime is 28137719. The next prime is 28137731. The reversal of 28137721 is 12773182.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 25110121 + 3027600 = 5011^2 + 1740^2 .

It is a cyclic number.

It is not a de Polignac number, because 28137721 - 2¹ = 28137719 is a prime.

Together with 28137719, it forms a pair of twin primes.

It is the 5305-th Hogben number.

It is not a weakly prime, because it can be changed into another prime (28137731) by changing a digit.

It is a nontrivial repunit in base 5304.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14068860 + 14068861.

It is an arithmetic number, because the mean of its divisors is an integer number (14068861).

Almost surely, 2^28137721 is an apocalyptic number.

It is an amenable number.

28137721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28137721 is an equidigital number, since it uses as much as digits as its factorization.

28137721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4704, while the sum is 31.

The square root of 28137721 is about 5304.5000706947. The cubic root of 28137721 is about 304.1559427590.

The spelling of 28137721 in words is "twenty-eight million, one hundred thirty-seven thousand, seven hundred twenty-one".