Quote:
Originally Posted by enzocreti
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
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Neither 20970!+1 nor 20970!-1 is semiprime, 20970!+1 = 7778806327 * C81510, and 20970!-1 = 4156001 * C81513