A022803 Numbers that reach ...,7,8,4,2,1 under the mapping: if n is even divide by 2 else add 1.

13, 14, 25, 26, 27, 28, 49, 50, 51, 52, 53, 54, 55, 56, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218

Offset

1,1

Comments

7 itself does not qualify, by decree. - N. J. A. Sloane, Sep 02 2017

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

nr7Q[n_]:=Module[{trms=NestWhileList[If[EvenQ[#], #/2, #+1]&, n, #!=1&]}, Length[ trms]>4 && trms[[-5]]==7]; Select[Range[8, 220], nr7Q] (* Harvey P. Dale, Oct 10 2017 *)

Prog

(PARI) xnp1(n, p) = { for(x=1, n, p1 = x; while(p1>1, if(p1%2==0, p1/=2, p1 = p1*p+1; ); if(p1==7, print1(x" ")) ) ) }

Crossrefs

Sequence in context: A336004 A296795 A079831 * A112653 A301660 A022103

Adjacent sequences: A022800 A022801 A022802 * A022804 A022805 A022806

Keyword

easy,nonn

Author

Cino Hilliard, Mar 23 2003

Status

approved