51638618021 has 2 divisors, whose sum is σ = 51638618022. Its totient is φ = 51638618020.

The previous prime is 51638617949. The next prime is 51638618023. The reversal of 51638618021 is 12081683615.

51638618021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 51205353796 + 433264225 = 226286^2 + 20815^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-51638618021 is a prime.

It is a super-2 number, since 2×51638618021² (a number of 22 digits) contains 22 as substring.

Together with 51638618023, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 51638618021.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51638618023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25819309010 + 25819309011.

It is an arithmetic number, because the mean of its divisors is an integer number (25819309011).

Almost surely, 2^51638618021 is an apocalyptic number.

It is an amenable number.

51638618021 is a deficient number, since it is larger than the sum of its proper divisors (1).

51638618021 is an equidigital number, since it uses as much as digits as its factorization.

51638618021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 69120, while the sum is 41.

The spelling of 51638618021 in words is "fifty-one billion, six hundred thirty-eight million, six hundred eighteen thousand, twenty-one".