21220111221581 has 2 divisors, whose sum is σ = 21220111221582. Its totient is φ = 21220111221580.

The previous prime is 21220111221559. The next prime is 21220111221679. The reversal of 21220111221581 is 18512211102212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19789374675625 + 1430736545956 = 4448525^2 + 1196134^2 .

It is a cyclic number.

It is not a de Polignac number, because 21220111221581 - 2²⁶ = 21220044112717 is a prime.

It is a super-2 number, since 2×21220111221581² (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 (21220111223581) 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 as a sum of consecutive naturals, namely, 10610055610790 + 10610055610791.

It is an arithmetic number, because the mean of its divisors is an integer number (10610055610791).

Almost surely, 2^{21220111221581} is an apocalyptic number.

It is an amenable number.

21220111221581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21220111221581 is an equidigital number, since it uses as much as digits as its factorization.

21220111221581 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1280, while the sum is 29.

Adding to 21220111221581 its reverse (18512211102212), we get a palindrome (39732322323793).

The spelling of 21220111221581 in words is "twenty-one trillion, two hundred twenty billion, one hundred eleven million, two hundred twenty-one thousand, five hundred eighty-one".