21211221210181 has 2 divisors, whose sum is σ = 21211221210182. Its totient is φ = 21211221210180.

The previous prime is 21211221210169. The next prime is 21211221210187. The reversal of 21211221210181 is 18101212211212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15145788114081 + 6065433096100 = 3891759^2 + 2462810^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21211221210181 is a prime.

It is a super-2 number, since 2×21211221210181² (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 (21211221210187) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605610605090 + 10605610605091.

It is an arithmetic number, because the mean of its divisors is an integer number (10605610605091).

Almost surely, 2^{21211221210181} is an apocalyptic number.

It is an amenable number.

21211221210181 is a deficient number, since it is larger than the sum of its proper divisors (1).

21211221210181 is an equidigital number, since it uses as much as digits as its factorization.

21211221210181 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 256, while the sum is 25.

Adding to 21211221210181 its reverse (18101212211212), we get a palindrome (39312433421393).

The spelling of 21211221210181 in words is "twenty-one trillion, two hundred eleven billion, two hundred twenty-one million, two hundred ten thousand, one hundred eighty-one".