28917821 has 2 divisors, whose sum is σ = 28917822. Its totient is φ = 28917820.

The previous prime is 28917797. The next prime is 28917839. The reversal of 28917821 is 12871982.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17935225 + 10982596 = 4235^2 + 3314^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-28917821 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (28917841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14458910 + 14458911.

It is an arithmetic number, because the mean of its divisors is an integer number (14458911).

Almost surely, 2^28917821 is an apocalyptic number.

It is an amenable number.

28917821 is a deficient number, since it is larger than the sum of its proper divisors (1).

28917821 is an equidigital number, since it uses as much as digits as its factorization.

28917821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16128, while the sum is 38.

The square root of 28917821 is about 5377.5292653783. The cubic root of 28917821 is about 306.9412012012.

The spelling of 28917821 in words is "twenty-eight million, nine hundred seventeen thousand, eight hundred twenty-one".