20516551021 has 2 divisors, whose sum is σ = 20516551022. Its totient is φ = 20516551020.

The previous prime is 20516551019. The next prime is 20516551067. The reversal of 20516551021 is 12015561502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17898693796 + 2617857225 = 133786^2 + 51165^2 .

It is a cyclic number.

It is not a de Polignac number, because 20516551021 - 2¹ = 20516551019 is a prime.

It is a super-2 number, since 2×20516551021² (a number of 21 digits) contains 22 as substring.

Together with 20516551019, 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 (20516551621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10258275510 + 10258275511.

It is an arithmetic number, because the mean of its divisors is an integer number (10258275511).

Almost surely, 2^20516551021 is an apocalyptic number.

It is an amenable number.

20516551021 is a deficient number, since it is larger than the sum of its proper divisors (1).

20516551021 is an equidigital number, since it uses as much as digits as its factorization.

20516551021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3000, while the sum is 28.

The spelling of 20516551021 in words is "twenty billion, five hundred sixteen million, five hundred fifty-one thousand, twenty-one".