# R/Unusual.R In kisungyou/Zseq: Integer Sequence Generator

#### Documented in Unusual

#' Unusual numbers
#'
#' Under OEIS \href{https://oeis.org/A064052}{A064052}, an \emph{Unusual} number is a natural number whose largest prime factor is strictly greater than square root of the number.
#' First 6 Unusual numbers are 2, 3, 5, 6, 7, 10.
#'
#'
#' @param n the number of first \code{n} entries from the sequence.
#' @param gmp a logical; \code{TRUE} to use large number representation, \code{FALSE} otherwise.
#'
#' @return a vector of length \code{n} containing first entries from the sequence.
#'
#' @examples
#' ## generate first 20 Unusual numbers
#' print(Unusual(20))
#'
#' @rdname A064052
#' @aliases A064052
#' @export
Unusual <- function(n, gmp=TRUE){
## Preprocessing for 'n'
n = check_n(n)

## Main Computation : first, compute in Rmpfr form
output = as.bigz(numeric(n))
output[1] = 2
if (n>1){
tgt = as.bigz(2)
iter = 1
while (iter<n){
tgt = tgt + 1
if (is.Unusual(tgt)){
iter = iter+1
output[iter] = tgt
}
}
}

## Rmpfr
if (!gmp){
output = as.integer(output)
}
return(output)
}

#' @keywords internal
#' @noRd
is.Unusual <- function(n){
maxpfac = max(gmp_divisors_prime(n))
if (maxpfac>sqrt(gmp::asNumeric(n))){
return(TRUE)
} else {
return(FALSE)
}
}

kisungyou/Zseq documentation built on Feb. 4, 2018, 12:02 a.m.