The last number (or 0 if there is none) in row n of the irregular triangle A177789 (Collatz related).
0, 1, 0, 3, 23, 0, 59, 219, 0, 999, 0, 4063, 8103, 0, 32603, 65439, 0, 262079, 0, 1047967, 2096879, 0, 8387431, 16776431, 0, 67107327, 134216703, 0, 536869615, 0, 2147482783, 4294966719, 0, 17179868415, 34359737983, 0, 137438953215, 0, 549755810847, 1099511627547
1
These terms closely track 2^n. See S000302 for the differences with 2^n. - T. D. Noe, Oct 15 2014
T. D. Noe, Plot of 40 terms
Eric W. Weisstein, Collatz Problem
(Mma) Collatz2[n_] := Most[NestWhileList[If[EvenQ[#], #/2, (3 # + 1)/2] &, n, # >= n &]]; Join[{0, 1, 0, 3, 23, 0, 59, 219, 0}, Table[d = Floor[2^(n/2)]; If[EvenQ[d], d--]; s = Select[Range[2^n - d, 2^n + d, 2], Length[Collatz2[#]] == n &]; If[Length[s] == 0, 0, 2^n - Select[2^n - s, # > 0 &][[-1]]], {n, 10, 40}]]
nonn
T. D. Noe, Oct 02 2014