A109404 - OEIS

%I #11 May 01 2014 08:41:05

%S 3,5,7,8,10,11,13,22,25,27,29,37,46,51,52,76,83,86,92,104,111,113,115,

%T 123,132,140,149,190,213,218,222,233,242,274,280,281,286,298,303,307,

%U 309,336,340,346,351,379,381,395,402,415,424,444,449,463,477,478,490

%N Numbers n such that sum of n-th and (n+1)-st semiprimes is a prime.

%e 3 is OK because sp(3)=9, sp(3)=10 and 9+10=19 (prime); sp(n)=n-th semiprime.

%t With[{semis=Partition[Select[Range[2000],PrimeOmega[#]==2&],2,1]}, Flatten[ Position[ semis,_?(PrimeQ[Total[#]]&),{1},Heads->False]]] (* _Harvey P. Dale_, May 01 2014 *)

%o (PARI) lista(nn) = {vec = vector(nn, i, i); sp = select(i->(bigomega(i)==2), vec); for (i = 1, #sp-1, if (isprime(sp[i]+sp[i+1]), print1(i, ", ")););} \\ _Michel Marcus_, Oct 06 2013

%Y Cf. A092191 = numbers n such that sum of n-th and (n+1)-st semiprimes is a semiprime.

%K nonn

%O 1,1

%A _Zak Seidov_, Jun 27 2005