**Prime number**

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

**Logic**

**Example**

Let's take a number 53 .

1. Calculate square root of 53 i.e. 7.28

2. Round 7.28 up i.e. 8

3. Divide 53 by each number between 2 and 8

(2,3,4,5,6,7,8)

4. You'll see there is always a remainder when 53 is divided by each number 2 and 8

5. Result :

**Prime****Excel Formula**

Suppose a value is entered in cell B4 . Paste the below formula in cell C4.

**CTRL + SHIFT + ENTER**to confirm this formula as an array formula. If done correctly, Excel will automatically place curly braces {...} around the formula.

**Download the workbook**

**Related Post**

**Counting Prime Numbers in an Interval with Excel**

**Generating Prime Numbers in an Interval with Excel**

Not working for 9. Problem with some indirect addressing.

ReplyDeleteIt is working fine for 9. Download the workbook (link provided in the article)

DeleteYour formula references A2, but doesn't say what I should be putting there. It's great that your formula works for your specific workbook, but if it can't be easily copied into another, then what is the point of publishing it.

DeleteAnonymous, it is very easily copied into any workbook, and it works exactly as advertised. The A2 reference makes no difference - a little investigation would have shown you that. And on that note, even if the formula wasn't directly translatable, would it really hurt to have to -gasp!- do a little of your own homework? There's a lot to learn from this post - that would be "the point" of publishing it.

Deletetry 1681 it says its prim but 41^2 = 1681

DeleteDoesn't seem to be 100% accurate, for example, For the input I entered 111,111,111. It said it was prime, although it can be divided by 9 and 3 at least. Any idea what may cause this kind of behavior? I don't really understand how the function works, so I can't diagnose the problem myself.

ReplyDeleteIt says 'Not Prime' for 111,111,111. You can save your workbook to any cloud drive and share link with me to debug.

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DeleteClever!! I never would have thought of using an array formula iterating along a virtual array to create a "for loop" inside an excel formula! I'm definitely going to have to remember that technique in the future!

ReplyDeleteThough, as evidenced by the comments, that technique is extremely advanced (and thus confusing) for most people. Perhaps a link to a post with an explanation of the technique would help.

Careful using this with numbers 81 and larger...

ReplyDeleteIt works fine for me. Make sure to press CTRL + SHIFT + ENTER after entering the formula but BEFORE clicking away. You will know that you entered it correctly if selecting the cell shows

Delete{=IF(B4=2,"Prime",IF(AND(MOD(B4,ROW(OFFSET($A$2,,,ROUNDUP(SQRT(B4),0)-1)))<>0),"Prime","Not Prime"))}

note the {} brackets.

Also note that entering the brackets manually does NOT work; you have to press CTRL + SHIFT + ENTER to get the brackets.

Shows 6 as a prime, not correct

ReplyDeleteThe formula works, the most common mistake is not making it an array formula by pressing Ctrl+Shift+Enter. If you don't make it an array formula it will return false positives (like 9, 81, and 1681).

DeleteThank you that is genius, works fine for me, shows 6 and 9 as prime.

ReplyDelete74 Prime

ReplyDelete75 Not Prime

76 Not Prime

77 Not Prime

78 Not Prime

79 Prime

80 Not Prime

81 Not Prime

82 Prime

83 Prime

84 Not Prime

85 Not Prime

86 Prime

87 Not Prime

88 Not Prime

89 Prime

90 Not Prime

91 Not Prime

92 Not Prime

93 Not Prime

94 Prime