cp's OEIS Frontend

A274048 a(n) = A116640(A018900(n)) = A116623(A059893(A018900(n))).

%I A274048 #20 Oct 25 2022 00:45:17
%S A274048 19,23,29,31,37,49,47,53,65,89,79,85,97,121,169,143,149,161,185,233,
%T A274048 329,271,277,289,313,361,457,649,527,533,545,569,617,713,905,1289,
%U A274048 1039,1045,1057,1081,1129,1225,1417,1801
%N A274048 a(n) = A116640(A018900(n)) = A116623(A059893(A018900(n))).
%C A274048 A subset of A116640 containing all terms A116640(m) such that m has binary weight of 2. This sequence is related to the Collatz and Terras trajectories; specifically those trajectories that include three odd numbers besides 1.
%F A274048 a(n) = 2^(Row(n)+1) + 3*(3+2^Col(n)) where Row(n) = A002024(n) = the row position of n when the sequence is viewed as a regular triangle; and Col(n) = A002260(n) = the column position of n when the sequence is viewed as a regular triangle.
%e A274048 The first three terms of A018900 are 3,5,6. Taking these terms from A116640 gives 19,23,29, which are the first three terms of this sequence. The sequence is generated from the regular triangle
%e A274048 1;
%e A274048 1,2;
%e A274048 1,2,3;
%e A274048 etc., so the first three terms are
%e A274048 2^(1+1) + 3*(3+2^1) = 19;
%e A274048 2^(2+1) + 3*(3+2^1) = 23;
%e A274048 2^(2+1) + 3*(3+2^2)= 29.
%Y A274048 Subsequence of A116640.
%Y A274048 Cf. A116623.
%K A274048 nonn,easy,tabl
%O A274048 1,1
%A A274048 _Joe Slater_, Jun 07 2016