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Numbers n such that prime(n)*prime(n+1) - 1 is semiprime.
7

%I #5 Apr 04 2016 13:29:30

%S 2,3,5,10,13,20,33,60,89,109,116,138,144,152,182,189,212,223,253,258,

%T 297,320,336,350,353,375,390,418,422,487,492,498,501,549,567,579,592,

%U 616,654,671,704,755,799,800,812,826,874,893,917,921,948,951,957,967

%N Numbers n such that prime(n)*prime(n+1) - 1 is semiprime.

%H Ray Chandler, <a href="/A103746/b103746.txt">Table of n, a(n) for n = 1..10000</a>

%e prime(10)*prime(11) - 1 = 29*31 - 1 = 898 = 2*449, hence 10 is a term.

%o (PARI) for(n=1,1000,if(bigomega(prime(n)*prime(n+1)-1)==2,print1(n,",")))

%Y Cf. A001358, A006881, A103533.

%K nonn,easy

%O 1,1

%A _Klaus Brockhaus_, Mar 29 2005