51720221 has 4 divisors (see below), whose sum is σ = 59108832. Its totient is φ = 44331612.

The previous prime is 51720199. The next prime is 51720247. The reversal of 51720221 is 12202715.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 51720221 - 2⁶ = 51720157 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 51720193 and 51720202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51725221) 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 in 3 ways as a sum of consecutive naturals, for example, 3694295 + ... + 3694308.

It is an arithmetic number, because the mean of its divisors is an integer number (14777208).

Almost surely, 2^51720221 is an apocalyptic number.

It is an amenable number.

51720221 is a deficient number, since it is larger than the sum of its proper divisors (7388611).

51720221 is an equidigital number, since it uses as much as digits as its factorization.

51720221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7388610.

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 51720221 is about 7191.6772035458. The cubic root of 51720221 is about 372.5805023975.

Adding to 51720221 its reverse (12202715), we get a palindrome (63922936).

The spelling of 51720221 in words is "fifty-one million, seven hundred twenty thousand, two hundred twenty-one".