A080706 Powers of 3 that reach ...,7,8,4,2,1 under the mapping: if n is even divide by 2 else add 1.

3, 8, 13, 15, 20, 25, 27, 32, 37, 44, 49, 54, 56, 61, 66, 68, 73, 78, 80, 85, 90, 97, 102, 107, 109, 114, 119, 121, 126, 131, 133, 138, 143, 150, 155, 160, 162, 167, 172, 174, 179, 184, 186, 191, 196, 203, 208, 213, 215, 220, 225, 227, 232, 237, 239, 244, 249

Offset

1,1

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Mathematica

okQ[n_]:=MemberQ[Partition[NestWhileList[If[EvenQ[#], #/2, #+1]&, 3^n, #!=1&], 5, 1], {7, 8, 4, 2, 1}]; Select[Range[250], okQ] (* Harvey P. Dale, Aug 22 2011 *)

Prog

(PARI) xnp3(n, p) = { for(x=1, n, p3 = 3^x; while(p3>1, if(p3%2==0, p3/=2, p3 = p3*p+1; ); if(p3==7, print1(x" ")) ) ) }

Crossrefs

Cf. A022803.

Sequence in context: A034260 A310291 A190551 * A190563 A310292 A024615

Adjacent sequences: A080703 A080704 A080705 * A080707 A080708 A080709

Keyword

easy,nonn

Author

Cino Hilliard, Mar 23 2003

Status

approved