55021721 has 2 divisors, whose sum is σ = 55021722. Its totient is φ = 55021720.

The previous prime is 55021717. The next prime is 55021723. The reversal of 55021721 is 12712055.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 52345225 + 2676496 = 7235^2 + 1636^2 .

It is a cyclic number.

It is not a de Polignac number, because 55021721 - 2² = 55021717 is a prime.

It is a Sophie Germain prime.

Together with 55021723, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (55021723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 27510860 + 27510861.

It is an arithmetic number, because the mean of its divisors is an integer number (27510861).

Almost surely, 2^55021721 is an apocalyptic number.

It is an amenable number.

55021721 is a deficient number, since it is larger than the sum of its proper divisors (1).

55021721 is an equidigital number, since it uses as much as digits as its factorization.

55021721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 700, while the sum is 23.

The square root of 55021721 is about 7417.6627720597. The cubic root of 55021721 is about 380.3453024753.

Adding to 55021721 its reverse (12712055), we get a palindrome (67733776).

The spelling of 55021721 in words is "fifty-five million, twenty-one thousand, seven hundred twenty-one".