OFFSET
0,2
COMMENTS
a(n) has the form 2*(q*3^n - 1) where q is the smallest odd number so that the alternating Collatz sequence of 2n+1 elements starting at 2*(q*2^n - 1) ends at the maximum of its Collatz trajectory.
Subsequence of a(n) when q=1 is a subsequence of A100774.
Conjecture: this sequence is infinite.
EXAMPLE
a(0) = 0 = 2*(1*3^0 - 1) since it is the start and end of the first alternating sequence of 1 element and the maximum of its trajectory.
a(5) = 9232 = 2*(19*3^5 - 1) is the last element in the first alternating sequence of 11 elements [1214, 607, 1822, 911, 2734, 1367, 4102, 2051, 6154, 3077, 9232] that ends in the trajectory maximum.
MATHEMATICA
(* we use function altdata[] from A277215 *)
a277874[n_]:=Map[#[[4]]&, altdata[2, n]]
Join[{0, 40}, a277874[29]] (*sequence data*)
CROSSREFS
KEYWORD
nonn
AUTHOR
Hartmut F. W. Hoft, Nov 03 2016
STATUS
approved