9991997 has 2 divisors, whose sum is σ = 9991998. Its totient is φ = 9991996.

The previous prime is 9991973. The next prime is 9992009. The reversal of 9991997 is 7991999.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 6205081 + 3786916 = 2491^2 + 1946^2 .

It is an emirp because it is prime and its reverse (7991999) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-9991997 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 (9991297) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4995998 + 4995999.

It is an arithmetic number, because the mean of its divisors is an integer number (4995999).

Almost surely, 2^9991997 is an apocalyptic number.

It is an amenable number.

9991997 is a deficient number, since it is larger than the sum of its proper divisors (1).

9991997 is an equidigital number, since it uses as much as digits as its factorization.

9991997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 413343, while the sum is 53.

The square root of 9991997 is about 3161.0120214893. The cubic root of 9991997 is about 215.3859805284.

It can be divided in two parts, 999 and 1997, that multiplied together give a triangular number (1995003 = T₁₉₉₇).

The spelling of 9991997 in words is "nine million, nine hundred ninety-one thousand, nine hundred ninety-seven".