#' @title Is a prime number?
#' @description Is n a prime number? You can see what is a
#' prime number [there](https://en.wikipedia.org/wiki/Prime_number).
#' @inheritParams primefactr-package
#' @examples
#' IsPrime(1) # FALSE
#' IsPrime(5) # TRUE
#' IsPrime(59999999) # TRUE
#' @return A boolean.
#' @export
IsPrime <- function(n) {
check(n)
if (n == 1) {
return(FALSE)
} else if (n == 2) {
return(TRUE)
} else {
return(all(n %% (2:sqrt(n)) != 0))
}
}
#' @title Get all prime numbers.
#' @description Get all prime numbers up to n.
#' @inheritParams primefactr-package
#' @examples
#' AllPrimesUpTo(10)
#' AllPrimesUpTo(100)
#' AllPrimesUpTo(1e6)
#' @return A integer vector of all prime numbers up to n.
#' @export
AllPrimesUpTo <- function(n) {
check(n)
primes <- rep(TRUE, n)
primes[1] <- FALSE
for (i in 1:sqrt(n)) {
if (primes[i]) primes[seq(i^2, n, i)] <- FALSE
}
which(primes)
}
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