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

19, 23, 29, 31, 37, 49, 47, 53, 65, 89, 79, 85, 97, 121, 169, 143, 149, 161, 185, 233, 329, 271, 277, 289, 313, 361, 457, 649, 527, 533, 545, 569, 617, 713, 905, 1289, 1039, 1045, 1057, 1081, 1129, 1225, 1417, 1801

Offset

1,1

Comments

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.

Links

Table of n, a(n) for n=1..44.

Formula

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.

Example

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
1;
1,2;
1,2,3;
etc., so the first three terms are
2^(1+1) + 3*(3+2^1) = 19;
2^(2+1) + 3*(3+2^1) = 23;
2^(2+1) + 3*(3+2^2)= 29.

Crossrefs

Subsequence of A116640.

Cf. A116623.

Sequence in context: A166061 A224534 A073319 * A334093 A120640 A309360

Adjacent sequences: A274045 A274046 A274047 * A274049 A274050 A274051

Keyword

nonn,easy,tabl

Author

Joe Slater, Jun 07 2016

Status

approved