99991987 has 2 divisors, whose sum is σ = 99991988. Its totient is φ = 99991986.

The previous prime is 99991981. The next prime is 99991999. The reversal of 99991987 is 78919999.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-99991987 is a prime.

It is not a weakly prime, because it can be changed into another prime (99991981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 49995993 + 49995994.

It is an arithmetic number, because the mean of its divisors is an integer number (49995994).

Almost surely, 2^99991987 is an apocalyptic number.

99991987 is a deficient number, since it is larger than the sum of its proper divisors (1).

99991987 is an equidigital number, since it uses as much as digits as its factorization.

99991987 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 99991987 is about 9999.5993419737. The cubic root of 99991987 is about 464.1464853463.

The spelling of 99991987 in words is "ninety-nine million, nine hundred ninety-one thousand, nine hundred eighty-seven".