55128721 has 2 divisors, whose sum is σ = 55128722. Its totient is φ = 55128720.

The previous prime is 55128679. The next prime is 55128727. The reversal of 55128721 is 12782155.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 32433025 + 22695696 = 5695^2 + 4764^2 .

It is a cyclic number.

It is not a de Polignac number, because 55128721 - 2²¹ = 53031569 is a prime.

It is not a weakly prime, because it can be changed into another prime (55128727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 27564360 + 27564361.

It is an arithmetic number, because the mean of its divisors is an integer number (27564361).

Almost surely, 2^55128721 is an apocalyptic number.

It is an amenable number.

55128721 is a deficient number, since it is larger than the sum of its proper divisors (1).

55128721 is an equidigital number, since it uses as much as digits as its factorization.

55128721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5600, while the sum is 31.

The square root of 55128721 is about 7424.8717834047. The cubic root of 55128721 is about 380.5916936226.

The spelling of 55128721 in words is "fifty-five million, one hundred twenty-eight thousand, seven hundred twenty-one".