21511355993 has 2 divisors, whose sum is σ = 21511355994. Its totient is φ = 21511355992.

The previous prime is 21511355941. The next prime is 21511356043. The reversal of 21511355993 is 39955311512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12956585929 + 8554770064 = 113827^2 + 92492^2 .

It is a cyclic number.

It is not a de Polignac number, because 21511355993 - 2²⁶ = 21444247129 is a prime.

It is not a weakly prime, because it can be changed into another prime (21511355893) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755677996 + 10755677997.

It is an arithmetic number, because the mean of its divisors is an integer number (10755677997).

Almost surely, 2^21511355993 is an apocalyptic number.

It is an amenable number.

21511355993 is a deficient number, since it is larger than the sum of its proper divisors (1).

21511355993 is an equidigital number, since it uses as much as digits as its factorization.

21511355993 is an evil number, because the sum of its binary digits is even.

The product of its digits is 182250, while the sum is 44.

The spelling of 21511355993 in words is "twenty-one billion, five hundred eleven million, three hundred fifty-five thousand, nine hundred ninety-three".