How to calculate random numerical sequency number? - php

Question

I'm trying to build the following numerical series 1, 1, 2, 3, 4, 5, 5, 6 until 100 ( It is a homework) . I have to do this using php code but I cannot get it , I've read the fibonacci method but the numerical series numbers are different.
<?php
$a=1;
$serie="1";
for ($i=1;$i<=100;$i++)
{
if($i%5==0)
{
$serie=$serie.",$i,$i";
}
else
{
$serie=$serie.",$i";
}
}
print $serie;
?>

Answer 1

As #tim pointed out in the comment, the solution is not printing a sequence from 1 to 100 where only numbers that are MOD 5 = 0 are duplicated. That way you do not get the repetition on 1.
From your homework question (which is not really clear in my opinion) I presume you want something like this:
<?php
for ($i = 0; $i < 100; $i++) {
echo $i+1 . ", ";
if ($i % 4 == 0) {
echo $i+1 . ", ";
}
}
?>
It prints:
1, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9, 10, 11, 12, 13, 13, 14, 15, 16, 17, 17, 18, 19, 20, 21, 21, 22, 23, 24, 25, 25, 26, 27, 28, 29, 29, 30, 31, 32, 33, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 41, 42, 43, 44, 45, 45, 46, 47, 48, 49, 49, 50, 51, 52, 53, 53, 54, 55, 56, 57, 57, 58, 59, 60, 61, 61, 62, 63, 64, 65, 65, 66, 67, 68, 69, 69, 70, 71, 72, 73, 73, 74, 75, 76, 77, 77, 78, 79, 80, 81, 81, 82, 83, 84, 85, 85, 86, 87, 88, 89, 89, 90, 91, 92, 93, 93, 94, 95, 96, 97, 97, 98, 99, 100,
The logic is to print the index increased by 1 each iteration, and print it again if the result of the modulus operation index % 4 is equal to 0.