6991203138221 has 2 divisors, whose sum is σ = 6991203138222. Its totient is φ = 6991203138220.

The previous prime is 6991203138203. The next prime is 6991203138239. The reversal of 6991203138221 is 1228313021996.

It is a balanced prime because it is at equal distance from previous prime (6991203138203) and next prime (6991203138239).

It can be written as a sum of positive squares in only one way, i.e., 6909595789321 + 81607348900 = 2628611^2 + 285670^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6991203138221 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6991203138121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3495601569110 + 3495601569111.

It is an arithmetic number, because the mean of its divisors is an integer number (3495601569111).

Almost surely, 2^{6991203138221} is an apocalyptic number.

It is an amenable number.

6991203138221 is a deficient number, since it is larger than the sum of its proper divisors (1).

6991203138221 is an equidigital number, since it uses as much as digits as its factorization.

6991203138221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 279936, while the sum is 47.

The spelling of 6991203138221 in words is "six trillion, nine hundred ninety-one billion, two hundred three million, one hundred thirty-eight thousand, two hundred twenty-one".