A008874 3x+1 sequence starting at 63.

63, 190, 95, 286, 143, 430, 215, 646, 323, 970, 485, 1456, 728, 364, 182, 91, 274, 137, 412, 206, 103, 310, 155, 466, 233, 700, 350, 175, 526, 263, 790, 395, 1186, 593, 1780, 890, 445, 1336, 668, 334, 167, 502, 251, 754, 377, 1132, 566, 283, 850, 425, 1276, 638, 319, 958, 479, 1438, 719, 2158, 1079

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

a(n) = A008875(n - 2) for n > 1.

Doesn't reach a power of 2 until a(103) = 16. - Alonso del Arte, May 18 2015

References

• Richard K. Guy, Unsolved Problems in Number Theory, E16.

Links

• T. D. Noe, Table of n, a(n) for n=0..107
• Index entries for sequences related to 3x+1 (or Collatz) problem

Crossrefs

Cf. A006370.

Row 63 of A347270.

Programs

Haskell

a008874 n = a008874_list !! n
a008874_list = 63 : iterate a006370 63
-- Reinhard Zumkeller, Aug 30 2012

Magma

[n eq 1 select 63 else IsOdd(Self(n-1)) select 3*Self(n-1)+1 else Self(n-1) div 2: n in [1..70]]; // Vincenzo Librandi, Jul 29 2014

Maple

f := proc(n) option remember; if n = 0 then 63; elif f(n-1) mod 2 = 0 then f(n-1)/2 else 3*f(n-1)+1; fi; end;

Mathematica

NestList[If[EvenQ[#], #/2, 3# + 1] &, 63, 100] (* Vincenzo Librandi, Jul 29 2014 *)

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Apr 27 2001