21001221181 has 2 divisors, whose sum is σ = 21001221182. Its totient is φ = 21001221180.

The previous prime is 21001221121. The next prime is 21001221203. The reversal of 21001221181 is 18112210012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11714815225 + 9286405956 = 108235^2 + 96366^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001221181 - 2¹⁵ = 21001188413 is a prime.

It is a super-2 number, since 2×21001221181² (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 (21001221121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500610590 + 10500610591.

It is an arithmetic number, because the mean of its divisors is an integer number (10500610591).

Almost surely, 2^21001221181 is an apocalyptic number.

It is an amenable number.

21001221181 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001221181 is an equidigital number, since it uses as much as digits as its factorization.

21001221181 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 64, while the sum is 19.

Adding to 21001221181 its reverse (18112210012), we get a palindrome (39113431193).

The spelling of 21001221181 in words is "twenty-one billion, one million, two hundred twenty-one thousand, one hundred eighty-one".