997991221 has 2 divisors, whose sum is σ = 997991222. Its totient is φ = 997991220.

The previous prime is 997991213. The next prime is 997991233. The reversal of 997991221 is 122199799.

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., 557620996 + 440370225 = 23614^2 + 20985^2 .

It is a cyclic number.

It is not a de Polignac number, because 997991221 - 2³ = 997991213 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (997991021) 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, 498995610 + 498995611.

It is an arithmetic number, because the mean of its divisors is an integer number (498995611).

Almost surely, 2^997991221 is an apocalyptic number.

It is an amenable number.

997991221 is a deficient number, since it is larger than the sum of its proper divisors (1).

997991221 is an equidigital number, since it uses as much as digits as its factorization.

997991221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 183708, while the sum is 49.

The square root of 997991221 is about 31590.9990503624. Note that the first 3 decimals coincide. The cubic root of 997991221 is about 999.3299581442.

The spelling of 997991221 in words is "nine hundred ninety-seven million, nine hundred ninety-one thousand, two hundred twenty-one".