51540021 has 24 divisors (see below), whose sum is σ = 80456376. Its totient is φ = 31605120.

The previous prime is 51539977. The next prime is 51540023. The reversal of 51540021 is 12004515.

It can be written as a sum of positive squares in 4 ways, for example, as 10400625 + 41139396 = 3225^2 + 6414^2 .

It is not a de Polignac number, because 51540021 - 2⁷ = 51539893 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 51539976 and 51540003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51540023) 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 23 ways as a sum of consecutive naturals, for example, 43051 + ... + 44231.

It is an arithmetic number, because the mean of its divisors is an integer number (3352349).

Almost surely, 2^51540021 is an apocalyptic number.

It is an amenable number.

51540021 is a deficient number, since it is larger than the sum of its proper divisors (28916355).

51540021 is a wasteful number, since it uses less digits than its factorization.

51540021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1573 (or 1570 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 51540021 is about 7179.1379008903. The cubic root of 51540021 is about 372.1472925220.

Adding to 51540021 its reverse (12004515), we get a palindrome (63544536).

The spelling of 51540021 in words is "fifty-one million, five hundred forty thousand, twenty-one".