997991021 has 2 divisors, whose sum is σ = 997991022. Its totient is φ = 997991020.

The previous prime is 997990993. The next prime is 997991053. The reversal of 997991021 is 120199799.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 609349225 + 388641796 = 24685^2 + 19714^2 .

It is an emirp because it is prime and its reverse (120199799) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 997991021 - 2²⁶ = 930882157 is a prime.

It is a super-3 number, since 3×997991021³ (a number of 28 digits) contains 333 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (997991221) 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, 498995510 + 498995511.

It is an arithmetic number, because the mean of its divisors is an integer number (498995511).

Almost surely, 2^997991021 is an apocalyptic number.

It is an amenable number.

997991021 is a deficient number, since it is larger than the sum of its proper divisors (1).

997991021 is an equidigital number, since it uses as much as digits as its factorization.

997991021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 91854, while the sum is 47.

The square root of 997991021 is about 31590.9958849037. The cubic root of 997991021 is about 999.3298913881.

The spelling of 997991021 in words is "nine hundred ninety-seven million, nine hundred ninety-one thousand, twenty-one".