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%I #13 Nov 11 2020 05:21:42
%S 4,6,9,25,10,15,34,21,14,35,22,33,49,38,39,26,51,55,74,69,46,65,57,58,
%T 85,93,62,115,86,91,87,82,77,106,95,111,94,119,118,129,133,121,141,
%U 146,143,122,145,142,123,155,134,161,158,169,166,205,177,178,183,194,187,159,202,201
%N a(1) = 4; thereafter a(n) is the least new semiprime such that a(n-1) + a(n) is a semiprime.
%C It is conjectured that every semiprime will appear.
%H Rémy Sigrist, <a href="/A338309/b338309.txt">Table of n, a(n) for n = 1..10000</a>
%H Rémy Sigrist, <a href="/A338309/a338309.gp.txt">PARI program for A338309</a>
%e 4+6 = 10 = A001358(4), 6+9 = 15 = A001358(6), 9+25 = 34 = A001358(12).
%t sp = Select[Range[4, 500], 2 == PrimeOmega[#] &]; s = {4}; a = 4;
%t Do[Do[b = sp[[k2]]; If[FreeQ[s, b] && 2 == PrimeOmega[a + b], AppendTo[s, (a = b)]; Break[]], {k2, Length[sp]}], {k1, 70}]; s
%o (PARI) See Links section.
%Y Cf. A001358.
%K nonn
%O 1,1
%A _Zak Seidov_, Oct 22 2020
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