21988545581 has 2 divisors, whose sum is σ = 21988545582. Its totient is φ = 21988545580.

The previous prime is 21988545571. The next prime is 21988545599. The reversal of 21988545581 is 18554588912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19927839556 + 2060706025 = 141166^2 + 45395^2 .

It is a cyclic number.

It is not a de Polignac number, because 21988545581 - 2¹⁴ = 21988529197 is a prime.

It is a super-2 number, since 2×21988545581² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21988545521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10994272790 + 10994272791.

It is an arithmetic number, because the mean of its divisors is an integer number (10994272791).

Almost surely, 2^21988545581 is an apocalyptic number.

It is an amenable number.

21988545581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21988545581 is an equidigital number, since it uses as much as digits as its factorization.

21988545581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4608000, while the sum is 56.

The spelling of 21988545581 in words is "twenty-one billion, nine hundred eighty-eight million, five hundred forty-five thousand, five hundred eighty-one".