A095385 Numbers n with property that n is a peak value in 3x+1 trajectory such that both n+1 and n-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

1,1

Comments

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

Links

Table of n, a(n) for n=1..43.

Example

n=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}

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}]

Crossrefs

Cf. A025586.

Sequence in context: A113839 A077112 A203537 * A071683 A192826 A190398

Adjacent sequences: A095382 A095383 A095384 * A095386 A095387 A095388

Keyword

nonn

Author

Labos Elemer, Jun 14 2004

Status

approved