cp's OEIS Frontend

A338901 Position of the first appearance of prime(n) as a factor in the list of squarefree semiprimes.

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