997939311821 has 2 divisors, whose sum is σ = 997939311822. Its totient is φ = 997939311820.

The previous prime is 997939311739. The next prime is 997939311827. The reversal of 997939311821 is 128113939799.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 985880197225 + 12059114596 = 992915^2 + 109814^2 .

It is a cyclic number.

It is not a de Polignac number, because 997939311821 - 2¹⁸ = 997939049677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (997939311827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 498969655910 + 498969655911.

It is an arithmetic number, because the mean of its divisors is an integer number (498969655911).

Almost surely, 2^997939311821 is an apocalyptic number.

It is an amenable number.

997939311821 is a deficient number, since it is larger than the sum of its proper divisors (1).

997939311821 is an equidigital number, since it uses as much as digits as its factorization.

997939311821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6613488, while the sum is 62.

The spelling of 997939311821 in words is "nine hundred ninety-seven billion, nine hundred thirty-nine million, three hundred eleven thousand, eight hundred twenty-one".