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%I #14 Jan 11 2021 02:50:33
%S 1,1,2,3,6,7,9,11,13,17,18,21,23,25,29,31,34,36,40,42,45,47,50,52,56,
%T 58,61,64,67,70,76,78,81,82,86,89,93,97,100,104,106,107,112,113,116,
%U 118,125,129,133,134,135,139,141,147,150,154,159,160,165,167,169
%N Position of the first appearance of prime(n) as a factor in the list of squarefree semiprimes.
%C The a(n)-th squarefree semiprime is the first divisible by prime(n).
%C After a(1) = 1, these are the positions of even terms in the list of all squarefree semiprimes A006881.
%H Amiram Eldar, <a href="/A338901/b338901.txt">Table of n, a(n) for n = 1..10000</a>
%F A006881(a(n)) = A100484(n).
%t rs=First/@FactorInteger[#]&/@Select[Range[100],SquareFreeQ[#]&&PrimeOmega[#]==2&];
%t Table[Position[rs,i][[1,1]],{i,Union@@rs}]
%Y A001358 lists semiprimes, with odds A046315 and evens A100484.
%Y A004526 counts 2-part partitions, with strict case A140106 (shifted left).
%Y A005117 lists squarefree numbers.
%Y A006881 lists squarefree semiprimes, with odds A046388 and evens A100484.
%Y A115392 is the not necessarily squarefree version.
%Y A166237 gives the first differences of squarefree semiprimes.
%Y A270650 and A270652 give the prime indices of squarefree semiprimes.
%Y A320656 counts factorizations into squarefree semiprimes.
%Y A338898 gives prime indices of semiprimes, with differences A176506.
%Y A338899 gives prime indices of squarefree semiprimes, differences A338900.
%Y A338912 and A338913 give the prime indices of semiprimes.
%Y Cf. A001221, A001222, A002100, A056239, A065516, A112798, A167171, A320891, A320911, A338903, A338905.
%K nonn
%O 1,3
%A _Gus Wiseman_, Nov 16 2020
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