21945773981 has 4 divisors (see below), whose sum is σ = 21948679452. Its totient is φ = 21942868512.

The previous prime is 21945773963. The next prime is 21945773987. The reversal of 21945773981 is 18937754912.

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 21528225625 + 417548356 = 146725^2 + 20434^2 .

It is a cyclic number.

It is not a de Polignac number, because 21945773981 - 2⁶ = 21945773917 is a prime.

It is a super-2 number, since 2×21945773981² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21945773987) 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, 1441376 + ... + 1456521.

It is an arithmetic number, because the mean of its divisors is an integer number (5487169863).

Almost surely, 2^21945773981 is an apocalyptic number.

It is an amenable number.

21945773981 is a deficient number, since it is larger than the sum of its proper divisors (2905471).

21945773981 is an equidigital number, since it uses as much as digits as its factorization.

21945773981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2905470.

The product of its digits is 3810240, while the sum is 56.

The spelling of 21945773981 in words is "twenty-one billion, nine hundred forty-five million, seven hundred seventy-three thousand, nine hundred eighty-one".