A095385 Numbers k with property that k is a peak value in 3x+1 trajectory such that both k+1 and k-1 are prime numbers.

4, 72, 180, 192, 228, 240, 312, 600, 1092, 1152, 1428, 1488, 1608, 1620, 1872, 2088, 2112, 2592, 2688, 3000, 3168, 3252, 3360, 3528, 4272, 4548, 4800, 5640, 6552, 6960, 7488, 7560, 8088, 8292, 8388, 8820, 9000, 9012, 9240, 9768, 10008, 10068, 10272

Offset: 1

Author

Labos Elemer, Jun 14 2004

Keywords

• nonn

Comments

In such cases it seems that initial value equals peak value. Proof needed!

Examples

			k=72: list={72,36,18,9,28,14,7,22,11,34,17,52,26,13,40,20,10,5,16,8,4,2,1}
		

Crossrefs

Intersection of A014574 and A025586.

Programs

Mathematica

c[x_]:=c[x]=(1-Mod[x, 2])*(x/2)+Mod[x, 2]*(3*x+1);c[1]=1; fpl[x_]:=FixedPointList[c, x]; {$RecursionLimit=1000;m=0}; Do[If[PrimeQ[1+Max[fpl[n]]]&&PrimeQ[ -1+Max[fpl[n]]], Print[n]], {n, 1, 10000}]