Same reason there was no such thing as Arctic Silver 4 thermal paste.
"Arctic Silver replied to me regarding my question of why they decided to skip the name of Arctic Silver 4 and decided to go straight from AS3 to AS5. The number 4 is not very comfortable with Asians since it sounds very similar to the word d**th and therefore to keep the interest of their Asian customers, they decided to not name the next AS compound AS4 but to AS5. Being Chinese myself, 4 is very badly connotated and it was a wise marketing strategy in both the customers and Arctic Silver's interest to skip naming their Arctic Silver compound Arctic Silver 4." http://www.slcentral.com/thermal-compound/page2.php
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Just scroll to the bottom of the page; all the answers are there.
Which would be more effective in the job search, learning another programming language or learning a real language?
Same reason there was no such thing as Arctic Silver 4 thermal paste. "Arctic Silver replied to me regarding my question of why they decided to skip the name of Arctic Silver 4 and decided to go straight from AS3 to AS5. The number 4 is not very comfortable with Asians since it sounds very similar to the word d**th and therefore to keep the interest of their Asian customers, they decided to not name the next AS compound AS4 but to AS5. Being Chinese myself, 4 is very badly connotated and it was a wise marketing strategy in both the customers and Arctic Silver's interest to skip naming their Arctic Silver compound Arctic Silver 4." http://www.slcentral.com/thermal-compound/page2.php