28312721 has 2 divisors, whose sum is σ = 28312722. Its totient is φ = 28312720.

The previous prime is 28312699. The next prime is 28312727. The reversal of 28312721 is 12721382.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 26122321 + 2190400 = 5111^2 + 1480^2 .

It is a cyclic number.

It is not a de Polignac number, because 28312721 - 2¹⁴ = 28296337 is a prime.

It is a super-2 number, since 2×28312721² = 1603220340847682, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (28312727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14156360 + 14156361.

It is an arithmetic number, because the mean of its divisors is an integer number (14156361).

Almost surely, 2^28312721 is an apocalyptic number.

It is an amenable number.

28312721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28312721 is an equidigital number, since it uses as much as digits as its factorization.

28312721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1344, while the sum is 26.

The square root of 28312721 is about 5320.9699303792. The cubic root of 28312721 is about 304.7851967802.

The spelling of 28312721 in words is "twenty-eight million, three hundred twelve thousand, seven hundred twenty-one".