31121821 has 2 divisors, whose sum is σ = 31121822. Its totient is φ = 31121820.

The previous prime is 31121819. The next prime is 31121833. The reversal of 31121821 is 12812113.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 29648025 + 1473796 = 5445^2 + 1214^2 .

It is a cyclic number.

It is not a de Polignac number, because 31121821 - 2¹ = 31121819 is a prime.

Together with 31121819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31121021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15560910 + 15560911.

It is an arithmetic number, because the mean of its divisors is an integer number (15560911).

Almost surely, 2^31121821 is an apocalyptic number.

It is an amenable number.

31121821 is a deficient number, since it is larger than the sum of its proper divisors (1).

31121821 is an equidigital number, since it uses as much as digits as its factorization.

31121821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 96, while the sum is 19.

The square root of 31121821 is about 5578.6934850375. The cubic root of 31121821 is about 314.5490178651.

Adding to 31121821 its reverse (12812113), we get a palindrome (43933934).

The spelling of 31121821 in words is "thirty-one million, one hundred twenty-one thousand, eight hundred twenty-one".