900009991 has 2 divisors, whose sum is σ = 900009992. Its totient is φ = 900009990.

The previous prime is 900009977. The next prime is 900010009. The reversal of 900009991 is 199900009.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 900009991 - 2⁵ = 900009959 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 900009991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (900009961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 450004995 + 450004996.

It is an arithmetic number, because the mean of its divisors is an integer number (450004996).

Almost surely, 2^900009991 is an apocalyptic number.

900009991 is a deficient number, since it is larger than the sum of its proper divisors (1).

900009991 is an equidigital number, since it uses as much as digits as its factorization.

900009991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6561, while the sum is 37.

The square root of 900009991 is about 30000.1665162045. The cubic root of 900009991 is about 965.4929572607.

The spelling of 900009991 in words is "nine hundred million, nine thousand, nine hundred ninety-one".