A103767 - OEIS

%I #7 Mar 15 2015 14:43:11

%S 6,10,29,42,44,55,57,102,104,111,120,136,174,184,257,269,308,325,327,

%T 401,426,504,514,565,571,594,595,652,717,755,864,882,901,907,985,1014,

%U 1074,1134,1141,1156,1198,1301,1327,1346,1362,1654,1670,1674,1778,1897

%N Numbers n such that prime(n)*prime(n+1)*prime(n+2) - 1 is semiprime.

%H Harvey P. Dale, <a href="/A103767/b103767.txt">Table of n, a(n) for n = 1..1000</a>

%e prime(10)*prime(11)*prime(12) - 1 = 29*31*37 - 1 = 33262= 2*16631, hence 10 is

%e a term.

%t PrimePi/@Transpose[Select[Partition[Prime[Range[2000]],3,1], PrimeOmega[ Times@@#-1]==2&]][[1]] (* _Harvey P. Dale_, Mar 15 2015 *)

%o (PARI) for(n=1,1900,if(bigomega(prime(n)*prime(n+1)*prime(n+2)-1)==2,print1(n,",")))

%Y Cf. A001358, A006881, A103614, A103746.

%K nonn,easy

%O 1,1

%A _Klaus Brockhaus_, Mar 29 2005