51257721 has 4 divisors (see below), whose sum is σ = 68343632. Its totient is φ = 34171812.

The previous prime is 51257719. The next prime is 51257743. The reversal of 51257721 is 12775215.

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 not a de Polignac number, because 51257721 - 2¹ = 51257719 is a prime.

It is a super-2 number, since 2×51257721² = 5254707924227682, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (51257021) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8542951 + ... + 8542956.

It is an arithmetic number, because the mean of its divisors is an integer number (17085908).

Almost surely, 2^51257721 is an apocalyptic number.

It is an amenable number.

51257721 is a deficient number, since it is larger than the sum of its proper divisors (17085911).

51257721 is a wasteful number, since it uses less digits than its factorization.

51257721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17085910.

The product of its digits is 4900, while the sum is 30.

The square root of 51257721 is about 7159.4497693608. The cubic root of 51257721 is about 371.4665944662.

The spelling of 51257721 in words is "fifty-one million, two hundred fifty-seven thousand, seven hundred twenty-one".