%I #4 Jan 06 2018 22:02:14
%S 82,106,111,178,194,226,287,314,327,371,395,411,538,543,586,591,611,
%T 623,674,687,695,746,767,791,794,815,818,898,951,995,1007,1043,1186,
%U 1226,1347,1418,1466,1514,1538,1546,1623,1631,1655,1703,1706,1851,1883,1906,1919
%N Take a squarefree semiprime and take the difference of its prime factors. If it is a squarefree semiprime repeat the process. Sequence lists the squarefree semiprimes that generate other squarefree semiprimes only in the first k steps of this process. Case k = 2.
%e 82 = 2*41, 41-2 = 39 = 3*13, 13-3 = 10 = 2*5 but 5-2 = 3 is not a squarefree semiprime.
%e 106 = 2*53, 53-2 = 51 = 3*17, 17-3 = 14 = 2*7 but 7-2 = 5 is not a squarefree semiprime.
%p with(numtheory): P:=proc(n,h) local a,j,ok; ok:=1; a:=n; for j from 1 to h doif issqrfree(a) and nops(factorset(a))=2 then a:=ifactors(a)[2]; a:=a[1][1]-a[2][1]; else ok:=0; break; fi; od;if ok=1 then n; fi; end: seq(P(i,3),i=1..2*10^3);
%Y Cf. A001358, A296096, A296808.
%K nonn,easy
%O 1,1
%A _Paolo P. Lava_, Dec 21 2017