This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A338909 #11 Nov 27 2020 02:06:39
%S A338909 9,21,25,39,49,57,65,87,91,111,115,121,129,133,159,169,183,185,203,
%T A338909 213,235,237,247,259,267,289,299,301,303,305,319,321,339,361,365,371,
%U A338909 377,393,417,427,445,453,481,489,497,515,517,519,529,543,551,553,559,565
%N A338909 Numbers of the form prime(x) * prime(y) where x and y have a common divisor > 1.
%F A338909 Equals A001358 \ A300912.
%F A338909 Equals A339002 \/ (A001248 \ {4}).
%e A338909 The sequence of terms together with their prime indices begins:
%e A338909 9: {2,2} 169: {6,6} 319: {5,10}
%e A338909 21: {2,4} 183: {2,18} 321: {2,28}
%e A338909 25: {3,3} 185: {3,12} 339: {2,30}
%e A338909 39: {2,6} 203: {4,10} 361: {8,8}
%e A338909 49: {4,4} 213: {2,20} 365: {3,21}
%e A338909 57: {2,8} 235: {3,15} 371: {4,16}
%e A338909 65: {3,6} 237: {2,22} 377: {6,10}
%e A338909 87: {2,10} 247: {6,8} 393: {2,32}
%e A338909 91: {4,6} 259: {4,12} 417: {2,34}
%e A338909 111: {2,12} 267: {2,24} 427: {4,18}
%e A338909 115: {3,9} 289: {7,7} 445: {3,24}
%e A338909 121: {5,5} 299: {6,9} 453: {2,36}
%e A338909 129: {2,14} 301: {4,14} 481: {6,12}
%e A338909 133: {4,8} 303: {2,26} 489: {2,38}
%e A338909 159: {2,16} 305: {3,18} 497: {4,20}
%t A338909 Select[Range[100],PrimeOmega[#]==2&&GCD@@PrimePi/@First/@FactorInteger[#]>1&]
%Y A338909 A082023 counts partitions with these as Heinz numbers, complement A023022.
%Y A338909 A300912 is the complement in A001358.
%Y A338909 A339002 is the squarefree case.
%Y A338909 A001221 counts distinct prime indices.
%Y A338909 A001222 counts prime indices.
%Y A338909 A001358 lists semiprimes, with odds A046315 and evens A100484.
%Y A338909 A004526 counts 2-part partitions, with strict case A140106 (shifted left).
%Y A338909 A006881 lists squarefree semiprimes, with odds A046388 and evens A100484.
%Y A338909 A176504/A176506/A087794 give sum/difference/product of semiprime indices.
%Y A338909 A318990 lists semiprimes with divisible indices.
%Y A338909 A320655 counts factorizations into semiprimes.
%Y A338909 A338898, A338912, and A338913 give semiprime indices.
%Y A338909 A338899, A270650, and A270652 give squarefree semiprime indices.
%Y A338909 A338910 lists semiprimes with odd indices.
%Y A338909 A338911 lists semiprimes with even indices.
%Y A338909 Cf. A005117, A037143, A055684, A056239, A065516, A112798, A115392, A128301, A289182, A338900, A338904.
%K A338909 nonn
%O A338909 1,1
%A A338909 _Gus Wiseman_, Nov 20 2020