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Old 2020-09-02, 16:35   #4
sweety439
 
Nov 2016

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Quote:
Originally Posted by enzocreti View Post
Is there an Oeis sequence dedicated to numbers n such that n!+1 and n!-1 are both semiprime? An example is 20970


Infact 20970!+1 is semiprime and also 20970!-1 is semi prime




No the example is wrong
Neither 20970!+1 nor 20970!-1 is semiprime, 20970!+1 = 7778806327 * C81510, and 20970!-1 = 4156001 * C81513
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