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euler25.php

@@ -4,5 +4,23 @@
 * https://projecteuler.net/problem=25
 */
 
+//see  https://fr.wikipedia.org/wiki/Suite_de_Fibonacci#Avec_la_formule_de_Binet
+echo intval((log(10)*999 + (log(5)/2) ) / log(1.61803398875)) +1;
 
-echo intval((log(10)*999 + (log(5)/2) ) / log(1.61803398875)) +1;
+/*
+Very long solution that didn't test :
+
+$i=1;
+$j=2;
+$count=2;
+while(strlen($i)<1000){
+    $new=gmp_add($i,$j);
+    $i=$j;
+    $j=$new;
+    $count++;
+}
+
+
+echo $count;
+
+*/