51221721 has 8 divisors (see below), whose sum is σ = 68731264. Its totient is φ = 33930000.

The previous prime is 51221717. The next prime is 51221741. The reversal of 51221721 is 12712215.

51221721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 51221721 - 2² = 51221717 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (51221741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 53905 + ... + 54846.

It is an arithmetic number, because the mean of its divisors is an integer number (8591408).

Almost surely, 2^51221721 is an apocalyptic number.

It is an amenable number.

51221721 is a deficient number, since it is larger than the sum of its proper divisors (17509543).

51221721 is a wasteful number, since it uses less digits than its factorization.

51221721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108911.

The product of its digits is 280, while the sum is 21.

The square root of 51221721 is about 7156.9351680730. The cubic root of 51221721 is about 371.3796096563.

Adding to 51221721 its reverse (12712215), we get a palindrome (63933936).

The spelling of 51221721 in words is "fifty-one million, two hundred twenty-one thousand, seven hundred twenty-one".