Comments on: [How-To] Check if a Number Is A Valid Credit Card Number

By: janesimpson

janesimpson — Sat, 26 Sep 2009 16:16:52 +0000

how would i check if a credit card is still valid…

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By: Best posts on Technofriends from 9th February - 15th February 2009 | Technofriends

Mon, 16 Feb 2009 08:31:25 +0000

[...] [How-To] Check if a Number Is A Valid Credit Card Number Posted on Monday, February 9th, 2009 in How-To – Comments: (11) The hack in this post makes use of Luhn’s algorithm which was developed by Hans Peter Luhn who was awarded US Patent 2950048 (”Computer for Verifying Numbers”) for the technique in 1960. In Practice, Using the Luhn’s algorithm, the last digit of the credit card number is arrived at. The same algorithm can be used to check if a number is actually a valid credit card number. [...]

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links for 2009-02-12 | Yostivanich.com — Thu, 12 Feb 2009 20:58:58 +0000

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By: Ryan Nejman

Ryan Nejman — Thu, 12 Feb 2009 07:12:25 +0000

Great post, but actually most are 16 digits or less, not more. All American Express numbers are only 15 digits in length. 17 or more digits are exceptionally rare, in fact I’ve never seen one and I’ve administered a database with literally millions of credit card numbers.

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BagOfNothing.com » Bag of Randomness — Wed, 11 Feb 2009 11:01:07 +0000

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By: Greg Jorgensen

Greg Jorgensen — Mon, 09 Feb 2009 18:26:42 +0000

Algorithm in Javascript, with explanation:
http://typicalprogrammer.com/?p=4

By: Michael Campbell

Michael Campbell — Mon, 09 Feb 2009 17:20:29 +0000

It works the same way, but I learned it instead of subtracting 9 from the product if it was greater than 10, you simply add all the digits. “10″ = 1 + 0; “14″ => 1 + 4, etc.