51905621 has 4 divisors (see below), whose sum is σ = 53695500. Its totient is φ = 50115744.

The previous prime is 51905611. The next prime is 51905629. The reversal of 51905621 is 12650915.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 41088100 + 10817521 = 6410^2 + 3289^2 .

It is a cyclic number.

It is not a de Polignac number, because 51905621 - 2²² = 47711317 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29), and also a Moran number because the ratio is a prime number: 1789849 = 51905621 / (5 + 1 + 9 + 0 + 5 + 6 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51905629) 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, 894896 + ... + 894953.

It is an arithmetic number, because the mean of its divisors is an integer number (13423875).

Almost surely, 2^51905621 is an apocalyptic number.

It is an amenable number.

51905621 is a deficient number, since it is larger than the sum of its proper divisors (1789879).

51905621 is a wasteful number, since it uses less digits than its factorization.

51905621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1789878.

The product of its (nonzero) digits is 2700, while the sum is 29.

The square root of 51905621 is about 7204.5555726915. Note that the first 4 decimals coincide. The cubic root of 51905621 is about 373.0251643951.

The spelling of 51905621 in words is "fifty-one million, nine hundred five thousand, six hundred twenty-one".