51656821 has 4 divisors (see below), whose sum is σ = 52631532. Its totient is φ = 50682112.

The previous prime is 51656791. The next prime is 51656833. The reversal of 51656821 is 12865615.

It is a happy number.

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 36360900 + 15295921 = 6030^2 + 3911^2 .

It is a cyclic number.

It is not a de Polignac number, because 51656821 - 2⁹ = 51656309 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 (51656851) 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, 487276 + ... + 487381.

It is an arithmetic number, because the mean of its divisors is an integer number (13157883).

Almost surely, 2^51656821 is an apocalyptic number.

It is an amenable number.

51656821 is a deficient number, since it is larger than the sum of its proper divisors (974711).

51656821 is an equidigital number, since it uses as much as digits as its factorization.

51656821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 974710.

The product of its digits is 14400, while the sum is 34.

The square root of 51656821 is about 7187.2679788637. The cubic root of 51656821 is about 372.4282005062.

The spelling of 51656821 in words is "fifty-one million, six hundred fifty-six thousand, eight hundred twenty-one".