28971721 has 2 divisors, whose sum is σ = 28971722. Its totient is φ = 28971720.

The previous prime is 28971643. The next prime is 28971739. The reversal of 28971721 is 12717982.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 28090000 + 881721 = 5300^2 + 939^2 .

It is a cyclic number.

It is not a de Polignac number, because 28971721 - 2⁹ = 28971209 is a prime.

It is a super-3 number, since 3×28971721³ (a number of 23 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (28971781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14485860 + 14485861.

It is an arithmetic number, because the mean of its divisors is an integer number (14485861).

Almost surely, 2^28971721 is an apocalyptic number.

It is an amenable number.

28971721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28971721 is an equidigital number, since it uses as much as digits as its factorization.

28971721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14112, while the sum is 37.

The square root of 28971721 is about 5382.5385274980. The cubic root of 28971721 is about 307.1317856680.

It can be divided in two parts, 28971 and 721, that added together give a palindrome (29692).

The spelling of 28971721 in words is "twenty-eight million, nine hundred seventy-one thousand, seven hundred twenty-one".