51591988621 has 2 divisors, whose sum is σ = 51591988622. Its totient is φ = 51591988620.

The previous prime is 51591988619. The next prime is 51591988633. The reversal of 51591988621 is 12688919515.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50867840521 + 724148100 = 225539^2 + 26910^2 .

It is a cyclic number.

It is not a de Polignac number, because 51591988621 - 2¹ = 51591988619 is a prime.

Together with 51591988619, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51591988681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25795994310 + 25795994311.

It is an arithmetic number, because the mean of its divisors is an integer number (25795994311).

Almost surely, 2^51591988621 is an apocalyptic number.

It is an amenable number.

51591988621 is a deficient number, since it is larger than the sum of its proper divisors (1).

51591988621 is an equidigital number, since it uses as much as digits as its factorization.

51591988621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1555200, while the sum is 55.

The spelling of 51591988621 in words is "fifty-one billion, five hundred ninety-one million, nine hundred eighty-eight thousand, six hundred twenty-one".