Palindromic primes in base 16: Difference between revisions
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if cols>0 then say '───────┼'center("" , 1 + cols*(w+1), '─') |
if cols>0 then say '───────┼'center("" , 1 + cols*(w+1), '─') |
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finds= 0; idx= 1 /*define # of palindromic primes & idx.*/ |
finds= 0; idx= 1 /*define # of palindromic primes & idx.*/ |
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$= /* |
$= /*hex palindromic primes (so far). */ |
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do j=1 for hidec; if \!.j then iterate /*J (decimal) not prime? Then skip.*/ |
do j=1 for hidec; if \!.j then iterate /*J (decimal) not prime? Then skip.*/ |
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x= d2x(j); if x\==reverse(x) then iterate /*Hex value not palindromic? " " */ |
x= d2x(j); if x\==reverse(x) then iterate /*Hex value not palindromic? " " */ |
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Revision as of 17:12, 23 June 2021
- Task
- Find palindromic primes in base 16, where n < 500
Factor
<lang factor>USING: kernel math.parser math.primes prettyprint sequences sequences.extras ;
500 primes-upto [ >hex ] [ dup reverse = ] map-filter .</lang>
- Output:
V{
"2"
"3"
"5"
"7"
"b"
"d"
"11"
"101"
"151"
"161"
"191"
"1b1"
"1c1"
}
Go
<lang go>package main
import (
"fmt" "rcu" "strconv" "strings"
)
func reverse(s string) string {
chars := []rune(s)
for i, j := 0, len(chars)-1; i < j; i, j = i+1, j-1 {
chars[i], chars[j] = chars[j], chars[i]
}
return string(chars)
}
func main() {
fmt.Println("Primes < 500 which are palindromic in base 16:")
primes := rcu.Primes(500)
count := 0
for _, p := range primes {
hp := strconv.FormatInt(int64(p), 16)
if hp == reverse(hp) {
fmt.Printf("%3s ", strings.ToUpper(hp))
count++
if count%5 == 0 {
fmt.Println()
}
}
}
fmt.Println("\n\nFound", count, "such primes.")
}</lang>
- Output:
Primes < 500 which are palindromic in base 16: 2 3 5 7 B D 11 101 151 161 191 1B1 1C1 Found 13 such primes.
REXX
<lang rexx>/*REXX program finds and displays palindromic primes for all N < 1000. */ parse arg hi cols . /*obtain optional argument from the CL.*/ if hi== | hi=="," then hi= 200 /*Not specified? Then use the default.*/ if cols== | cols=="," then cols= 10 /* " " " " " " */ hidec= x2d(hi) /*obtain the decimal value of hi (hex).*/ call genP /*build array of semaphores for primes.*/ w= 8 /*max width of a number in any column. */ title= ' palindromic primes in base 16 that are < ' hi if cols>0 then say ' index │'center(title, 1 + cols*(w+1) ) if cols>0 then say '───────┼'center("" , 1 + cols*(w+1), '─') finds= 0; idx= 1 /*define # of palindromic primes & idx.*/ $= /*hex palindromic primes (so far). */
do j=1 for hidec; if \!.j then iterate /*J (decimal) not prime? Then skip.*/ x= d2x(j); if x\==reverse(x) then iterate /*Hex value not palindromic? " " */ finds= finds + 1 /*bump the number of palindromic primes*/ if cols<0 then iterate /*Build the list (to be shown later)? */ $= $ right( lowerHex(x), w) /*use a lowercase version of the hex #.*/ if finds//cols\==0 then iterate /*have we populated a line of output? */ say center(idx, 7)'│' substr($, 2); $= /*display what we have so far (cols). */ idx= idx + cols /*bump the index count for the output*/ end /*j*/
if $\== then say center(idx, 7)"│" substr($, 2) /*possible display residual output.*/ if cols>0 then say '───────┴'center("" , 1 + cols*(w+1), '─') say say 'Found ' finds title exit 0 /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ lowerHex: return translate( arg(1), 'abcdef', "ABCDEF") /*convert hex chars──►lowercase.*/ /*──────────────────────────────────────────────────────────────────────────────────────*/ genP: !.= 0; hprime= max(hidec, reverse(hidec)) /*placeholders for primes (semaphores).*/
@.1=2; @.2=3; @.3=5; @.4=7; @.5=11 /*define some low primes. */
!.2=1; !.3=1; !.5=1; !.7=1; !.11=1 /* " " " " flags. */
#=5; s.#= @.# **2 /*number of primes so far; prime². */
/* [↓] generate more primes ≤ high.*/
do j=@.#+2 by 2 to hprime /*find odd primes from here on. */
parse var j -1 _; if _==5 then iterate /*J divisible by 5? (right dig)*/
if j// 3==0 then iterate /*" " " 3? */
if j// 7==0 then iterate /*" " " 7? */
/* [↑] the above 3 lines saves time.*/
do k=5 while s.k<=j /* [↓] divide by the known odd primes.*/
if j // @.k == 0 then iterate j /*Is J ÷ X? Then not prime. ___ */
end /*k*/ /* [↑] only process numbers ≤ √ J */
#= #+1; @.#= j; s.#= j*j; !.j= 1 /*bump # of Ps; assign next P; P²; P# */
end /*j*/; return</lang>
- output when using the default inputs:
index │ palindromic primes in base 16 that are < 200 ───────┼─────────────────────────────────────────────────────────────────────────────────────────── 1 │ 2 3 5 7 b d 11 101 151 161 11 │ 191 1b1 1c1 ───────┴─────────────────────────────────────────────────────────────────────────────────────────── Found 13 palindromic primes in base 16 that are < 200
Ring
<lang ring> load "stdlib.ring" see "working..." + nl see "Palindromic primes in base 16:" + nl row = 0 decList = 0:15 baseList = ["0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"] limit = 500
for n = 1 to limit
hex = hex(n)
if ispalindrome(hex) and isprime(n)
see "" + upper(hex) + " "
row = row + 1
if row%5 = 0
see nl
ok
ok
next
see nl + "Found " + row + " palindromic primes in base 16" + nl see "done..." + nl </lang>
- Output:
working... Palindromic primes in base 16: 2 3 5 7 B D 11 101 151 161 191 1B1 1C1 Found 13 palindromic primes in base 16 done...
Wren
<lang ecmascript>import "/math" for Int import "/fmt" for Conv, Fmt
System.print("Primes < 500 which are palindromic in base 16:") var primes = Int.primeSieve(500) var count = 0 for (p in primes) {
var hp = Conv.Itoa(p, 16)
if (hp == hp[-1..0]) {
Fmt.write("$3s ", hp)
count = count + 1
if (count % 5 == 0) System.print()
}
} System.print("\n\nFound %(count) such primes.")</lang>
- Output:
Primes < 500 which are palindromic in base 16: 2 3 5 7 B D 11 101 151 161 191 1B1 1C1 Found 13 such primes.