21213543326581 has 2 divisors, whose sum is σ = 21213543326582. Its totient is φ = 21213543326580.

The previous prime is 21213543326567. The next prime is 21213543326639. The reversal of 21213543326581 is 18562334531212.

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., 16117535062225 + 5096008264356 = 4014665^2 + 2257434^2 .

It is a cyclic number.

It is not a de Polignac number, because 21213543326581 - 2³³ = 21204953391989 is a prime.

It is a super-2 number, since 2×21213543326581² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21213543326531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606771663290 + 10606771663291.

It is an arithmetic number, because the mean of its divisors is an integer number (10606771663291).

Almost surely, 2^{21213543326581} is an apocalyptic number.

It is an amenable number.

21213543326581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21213543326581 is an equidigital number, since it uses as much as digits as its factorization.

21213543326581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1036800, while the sum is 46.

Adding to 21213543326581 its reverse (18562334531212), we get a palindrome (39775877857793).

The spelling of 21213543326581 in words is "twenty-one trillion, two hundred thirteen billion, five hundred forty-three million, three hundred twenty-six thousand, five hundred eighty-one".