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%I #13 Jan 06 2021 16:17:44
%S 21,39,57,87,91,111,129,133,159,183,203,213,237,247,259,267,301,303,
%T 321,339,371,377,393,417,427,453,481,489,497,519,543,551,553,559,579,
%U 597,623,669,687,689,703,707,717,749,753,789,791,793,813,817,843,879,917
%N Numbers of the form prime(x) * prime(y) where x and y are distinct and both even.
%C The squarefree semiprimes in A332821. - _Peter Munn_, Dec 25 2020
%F Numbers m such that A001221(m) = A001222(m) = 2 and A195017(m) = -2. - _Peter Munn_, Dec 31 2020
%e The sequence of terms together with their prime indices begins:
%e 21: {2,4} 267: {2,24} 543: {2,42}
%e 39: {2,6} 301: {4,14} 551: {8,10}
%e 57: {2,8} 303: {2,26} 553: {4,22}
%e 87: {2,10} 321: {2,28} 559: {6,14}
%e 91: {4,6} 339: {2,30} 579: {2,44}
%e 111: {2,12} 371: {4,16} 597: {2,46}
%e 129: {2,14} 377: {6,10} 623: {4,24}
%e 133: {4,8} 393: {2,32} 669: {2,48}
%e 159: {2,16} 417: {2,34} 687: {2,50}
%e 183: {2,18} 427: {4,18} 689: {6,16}
%e 203: {4,10} 453: {2,36} 703: {8,12}
%e 213: {2,20} 481: {6,12} 707: {4,26}
%e 237: {2,22} 489: {2,38} 717: {2,52}
%e 247: {6,8} 497: {4,20} 749: {4,28}
%e 259: {4,12} 519: {2,40} 753: {2,54}
%t Select[Range[100],SquareFreeQ[#]&&PrimeOmega[#]==2&&OddQ[Times@@(1+ PrimePi/@First/@FactorInteger[#])]&]
%Y A338911 is the not necessarily squarefree version.
%Y A339003 is the odd instead of even version, with not necessarily squarefree version A338910.
%Y A001358 lists semiprimes, with odd/even terms A046315/A100484.
%Y A005117 lists squarefree numbers.
%Y A006881 lists squarefree semiprimes, with odd/even terms A046388/A100484.
%Y A289182/A115392 list the positions of odd/even terms in A001358.
%Y A300912 lists products of pairs of primes with relatively prime indices.
%Y A318990 lists products of pairs of primes with divisible indices.
%Y A320656 counts factorizations into squarefree semiprimes.
%Y A338898, A338912, and A338913 give the prime indices of semiprimes, with product A087794, sum A176504, and difference A176506.
%Y A338899, A270650, and A270652 give the prime indices of squarefree semiprimes, with difference A338900.
%Y A338904 groups semiprimes by weight.
%Y A338906/A338907 list semiprimes of even/odd weight.
%Y Cf. A000040, A001221, A001222, A056239, A112798, A166237, A195017, A320911, A338901, A338903, A339002.
%Y Subsequence of A332821.
%K nonn
%O 1,1
%A _Gus Wiseman_, Nov 22 2020
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