9915991 has 2 divisors, whose sum is σ = 9915992. Its totient is φ = 9915990.

The previous prime is 9915979. The next prime is 9916003. The reversal of 9915991 is 1995199.

It is a balanced prime because it is at equal distance from previous prime (9915979) and next prime (9916003).

It is a cyclic number.

It is not a de Polignac number, because 9915991 - 2¹⁹ = 9391703 is a prime.

9915991 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9915911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4957995 + 4957996.

It is an arithmetic number, because the mean of its divisors is an integer number (4957996).

Almost surely, 2^9915991 is an apocalyptic number.

9915991 is a deficient number, since it is larger than the sum of its proper divisors (1).

9915991 is an equidigital number, since it uses as much as digits as its factorization.

9915991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 32805, while the sum is 43.

The square root of 9915991 is about 3148.9666559048. The cubic root of 9915991 is about 214.8384652889.

The spelling of 9915991 in words is "nine million, nine hundred fifteen thousand, nine hundred ninety-one".