21054947581 has 4 divisors (see below), whose sum is σ = 21121367292. Its totient is φ = 20988527872.

The previous prime is 21054947531. The next prime is 21054947591. The reversal of 21054947581 is 18574945012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7381387225 + 13673560356 = 85915^2 + 116934^2 .

It is a cyclic number.

It is not a de Polignac number, because 21054947581 - 2¹¹ = 21054945533 is a prime.

It is a super-2 number, since 2×21054947581² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21054947531) 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 in 3 ways as a sum of consecutive naturals, for example, 33209380 + ... + 33210013.

It is an arithmetic number, because the mean of its divisors is an integer number (5280341823).

Almost surely, 2^21054947581 is an apocalyptic number.

It is an amenable number.

21054947581 is a deficient number, since it is larger than the sum of its proper divisors (66419711).

21054947581 is an equidigital number, since it uses as much as digits as its factorization.

21054947581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66419710.

The product of its (nonzero) digits is 403200, while the sum is 46.

The spelling of 21054947581 in words is "twenty-one billion, fifty-four million, nine hundred forty-seven thousand, five hundred eighty-one".