31221220181 has 2 divisors, whose sum is σ = 31221220182. Its totient is φ = 31221220180.

The previous prime is 31221220127. The next prime is 31221220237. The reversal of 31221220181 is 18102212213.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 29713140625 + 1508079556 = 172375^2 + 38834^2 .

It is a cyclic number.

It is not a de Polignac number, because 31221220181 - 2⁶ = 31221220117 is a prime.

It is a super-2 number, since 2×31221220181² (a number of 22 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31227220181) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15610610090 + 15610610091.

It is an arithmetic number, because the mean of its divisors is an integer number (15610610091).

Almost surely, 2^31221220181 is an apocalyptic number.

It is an amenable number.

31221220181 is a deficient number, since it is larger than the sum of its proper divisors (1).

31221220181 is an equidigital number, since it uses as much as digits as its factorization.

31221220181 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 384, while the sum is 23.

Adding to 31221220181 its reverse (18102212213), we get a palindrome (49323432394).

The spelling of 31221220181 in words is "thirty-one billion, two hundred twenty-one million, two hundred twenty thousand, one hundred eighty-one".