55205721 has 24 divisors (see below), whose sum is σ = 82653480. Its totient is φ = 35502720.

The previous prime is 55205677. The next prime is 55205767. The reversal of 55205721 is 12750255.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 39690000 + 15515721 = 6300^2 + 3939^2 .

It is not a de Polignac number, because 55205721 - 2¹⁰ = 55204697 is a prime.

It is a super-2 number, since 2×55205721² = 6095343262259682, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (55205321) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 620245 + ... + 620333.

It is an arithmetic number, because the mean of its divisors is an integer number (3443895).

Almost surely, 2^55205721 is an apocalyptic number.

It is an amenable number.

55205721 is a deficient number, since it is larger than the sum of its proper divisors (27447759).

55205721 is an frugal number, since it uses more digits than its factorization.

55205721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 218 (or 133 counting only the distinct ones).

The product of its (nonzero) digits is 3500, while the sum is 27.

The square root of 55205721 is about 7430.0552487852. The cubic root of 55205721 is about 380.7688059424.

Adding to 55205721 its reverse (12750255), we get a palindrome (67955976).

The spelling of 55205721 in words is "fifty-five million, two hundred five thousand, seven hundred twenty-one".