51808021 has 4 divisors (see below), whose sum is σ = 51962092. Its totient is φ = 51653952.

The previous prime is 51808013. The next prime is 51808039. The reversal of 51808021 is 12080815.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12080815 = 5 ⋅2416163.

It can be written as a sum of positive squares in 2 ways, for example, as 21436900 + 30371121 = 4630^2 + 5511^2 .

It is a cyclic number.

It is not a de Polignac number, because 51808021 - 2³ = 51808013 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51808091) 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, 76530 + ... + 77203.

It is an arithmetic number, because the mean of its divisors is an integer number (12990523).

Almost surely, 2^51808021 is an apocalyptic number.

It is an amenable number.

51808021 is a deficient number, since it is larger than the sum of its proper divisors (154071).

51808021 is a wasteful number, since it uses less digits than its factorization.

51808021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 154070.

The product of its (nonzero) digits is 640, while the sum is 25.

The square root of 51808021 is about 7197.7788935199. The cubic root of 51808021 is about 372.7912135018.

Adding to 51808021 its reverse (12080815), we get a palindrome (63888836).

The spelling of 51808021 in words is "fifty-one million, eight hundred eight thousand, twenty-one".