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Talk:Emirp primes: Difference between revisions
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:: It is probably faster not to calculate the list starting with 9 but to test for primeality when a Candidate in the 3 lists starting with 1, 3, or 7 ends in a 9.--[[User:Nigel Galloway|Nigel Galloway]] ([[User talk:Nigel Galloway|talk]]) 13:51, 27 March 2014 (UTC)
::: When counting Emirps, one using trial division could use the fact, that Emirps out of 10..01 to 19..99 are mirrored in 9...1,7....1,3...1 and 1...1.What does this mean. I don't need to test numbers ending with "1" when I count them while testing 1....., so 3.... only needs to test Emirp for last digit element of '3,7,9' after that 7...... need tests only for '7,9', at least 9.... need only test for last digit = 9.That nearly halves the tests needed.
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