1009991 has 2 divisors, whose sum is σ = 1009992. Its totient is φ = 1009990.

The previous prime is 1009963. The next prime is 1009993. The reversal of 1009991 is 1999001.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1009991 - 2⁶ = 1009927 is a prime.

Together with 1009993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1009993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 504995 + 504996.

It is an arithmetic number, because the mean of its divisors is an integer number (504996).

2^1009991 is an apocalyptic number.

1009991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1009991 is an equidigital number, since it uses as much as digits as its factorization.

1009991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 729, while the sum is 29.

The square root of 1009991 is about 1004.9830844348. The cubic root of 1009991 is about 100.3319303368.

The spelling of 1009991 in words is "one million, nine thousand, nine hundred ninety-one".