21209331518881 has 81 divisors (see below), whose sum is σ = 24744199437363. Its totient is φ = 18164272753440.

The previous prime is 21209331518861. The next prime is 21209331518939. The reversal of 21209331518881 is 18881513390212.

The square root of 21209331518881 is 4605359.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 14782802315281 + 6426529203600 = 3844841^2 + 2535060^2 .

It is not a de Polignac number, because 21209331518881 - 2²¹ = 21209329421729 is a prime.

It is a super-2 number, since 2×21209331518881² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21209331518861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 80 ways as a sum of consecutive naturals, for example, 127001985060 + ... + 127001985226.

Almost surely, 2^{21209331518881} is an apocalyptic number.

21209331518881 is the 4605359-th square number.

21209331518881 is the 2302680-th centered octagonal number.

It is an amenable number.

21209331518881 is a deficient number, since it is larger than the sum of its proper divisors (3534867918482).

21209331518881 is an equidigital number, since it uses as much as digits as its factorization.

21209331518881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 620 (or 310 counting only the distinct ones).

The product of its (nonzero) digits is 829440, while the sum is 52.

The spelling of 21209331518881 in words is "twenty-one trillion, two hundred nine billion, three hundred thirty-one million, five hundred eighteen thousand, eight hundred eighty-one".