OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
51 is in the sequence because 51 = 3*17, the next semiprime is 55 = 5*11, and 51+55 = 106 = 2*53, is also semiprime.
MATHEMATICA
s[n_] := PrimeOmega@n == 2; L = Select[Range@480, s]; Pick[ Most@L, s /@ (Plus @@@ Partition[L, 2, 1])] (* Giovanni Resta, Apr 25 2016 *)
Select[Partition[Select[Range[500], PrimeOmega[#]==2&], 2, 1], PrimeOmega[ Total[ #]] == 2&][[All, 1]] (* Harvey P. Dale, Jul 10 2018 *)
PROG
(PARI) proxsem(n)=my(p=n, s, r); while(s==0, p++; if(bigomega(p)==2, s=1; r=p)); p
{for(i=1, 500, if(bigomega(i)==2, a=proxsem(i); if(bigomega(a+i)==2, print1(i, ", "))))}
(PARI) issemi(n)=bigomega(n)==2
list(lim)=my(v=List(), u=v); lim\=1; while(bigomega(lim++)!=2, ); forprime(p=2, lim\2, forprime(q=2, lim\p, listput(v, p*q))); v=Set(v); for(i=1, #v-1, if(issemi(v[i+1]+v[i]), listput(u, v[i]))); Set(u) \\ Charles R Greathouse IV, Apr 29 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Antonio Roldán, Apr 25 2016
STATUS
approved