99987991 has 2 divisors, whose sum is σ = 99987992. Its totient is φ = 99987990.

The previous prime is 99987983. The next prime is 99987997. The reversal of 99987991 is 19978999.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 99987991 - 2³ = 99987983 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (99987997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 49993995 + 49993996.

It is an arithmetic number, because the mean of its divisors is an integer number (49993996).

Almost surely, 2^99987991 is an apocalyptic number.

99987991 is a deficient number, since it is larger than the sum of its proper divisors (1).

99987991 is an equidigital number, since it uses as much as digits as its factorization.

99987991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3306744, while the sum is 61.

The square root of 99987991 is about 9999.3995319719. The cubic root of 99987991 is about 464.1403023374.

The spelling of 99987991 in words is "ninety-nine million, nine hundred eighty-seven thousand, nine hundred ninety-one".