# RogerBW's Blog

 Perl Weekly Challenge 41: obscure number sequences 23 January 2020 I’ve been doing the Perl Weekly Challenges. The latest was about generating number sequences. Part 1 is to list the attractive numbers (having a list of prime factors that itself contains a prime number of entries) that lie between 1 and 50 inclusive. I'm using my private set of rules for these challenges, which is that it's OK to use Perl5 modules as long as they solve only part of the problem (having a solution that's just a function call is no fun), but Perl6 should work with what's available in the language core (since it's so much larger). So for Perl5: ``````use Math::Prime::Util qw(factor is_prime); foreach my \$c (1..50) { if (is_prime(scalar factor(\$c))) { print "\$c\n"; } } `````` Meanwhile in Perl6 I build a list of relevant primes (and a hash of it so that I can look things up in it quickly), then factorise by trial modulo (inefficient, but with numbers this small it really doesn't matter). ``````my \$top=50; my @factors=grep {is-prime(\$_)}, (1..\$top); my %pc=map {\$_ => 1}, @factors; for (1..\$top) -> \$c { my \$cc=\$c; my \$cn=0; my @ff=@factors; while (\$cc != 1 && !(%pc{\$c}:exists)) { my \$l=@ff[0]; while (\$cc % @ff[0] == 0) { \$cn++; \$cc /= @ff[0]; } shift @ff; } if (%pc{\$c}:exists) { \$cn++; } if (%pc{\$cn}:exists) { say \$c; } } `````` Part 2 asks for the first twenty Leonardo numbers (calculated like Fibonacci numbers after the first two, but adding 1 each time, so 1, 1, 3, 5, 9, …). ``````my @stack; foreach my \$i (0..19) { if (\$i<2) { push @stack,1; } else { push @stack,1+\$stack[-1]+\$stack[-2]; shift @stack; } print \$stack[-1],"\n"; } `````` I don't really need that `shift @stack`, but putting it in allows the number limit to be set as high as I like without risking running out of memory. Perl6 in this case works the same way, but using `@stack[@stack.end]` rather than `\$stack[-1]`. Comments on this post are now closed. If you have particular grounds for adding a late comment, comment on a more recent post quoting the URL of this one. Search 10 per page 20 per page 50 per page 100 per page Archive Tags 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s 3d printing action advent of code aeronautics aikakirja anecdote animation anime army astronomy audio audio tech aviation base commerce battletech beer boardgaming book of the week bookmonth chain of command children chris chronicle church of no redeeming virtues cold war comedy computing contemporary cornish smuggler cosmic encounter coup covid-19 crime cthulhu eternal cycling dead of winter doctor who documentary drama driving drone ecchi economics en garde espionage essen 2015 essen 2016 essen 2017 essen 2018 essen 2019 essen 2022 essen 2023 existential risk falklands war fandom fanfic fantasy feminism film firefly first world war flash point flight simulation food garmin drive gazebo genesys geocaching geodata gin gkp gurps gurps 101 gus harpoon historical history horror hugo 2014 hugo 2015 hugo 2016 hugo 2017 hugo 2018 hugo 2019 hugo 2020 hugo 2022 hugo-nebula reread in brief avoid instrumented life javascript julian simpson julie enfield kickstarter kotlin learn to play leaving earth linux liquor lovecraftiana lua mecha men with beards mpd museum music mystery naval noir non-fiction one for the brow opera parody paul temple perl perl weekly challenge photography podcast politics postscript powers prediction privacy project woolsack pyracantha python quantum rail raku ranting raspberry pi reading reading boardgames social real life restaurant reviews romance rpg a day rpgs ruby rust scala science fiction scythe second world war security shipwreck simutrans smartphone south atlantic war squaddies stationery steampunk stuarts suburbia superheroes suspense television the resistance the weekly challenge thirsty meeples thriller tin soldier torg toys trailers travel type 26 type 31 type 45 vietnam war war wargaming weather wives and sweethearts writing about writing x-wing young adult Special All book reviews, All film reviews
Produced by aikakirja v0.1