A070870 a(1) = 6; a(n+1) = (a(n)+1)/2 if a(n) odd, or 5*a(n)/2 if a(n) even.

6, 15, 8, 20, 50, 125, 63, 32, 80, 200, 500, 1250, 3125, 1563, 782, 1955, 978, 2445, 1223, 612, 1530, 3825, 1913, 957, 479, 240, 600, 1500, 3750, 9375, 4688, 11720, 29300, 73250, 183125, 91563, 45782, 114455, 57228, 143070, 357675, 178838

Offset

1,1

References

S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 123.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Eric Weisstein, Wolfram Sequences

Example

a(5)=125 is odd, so a(6)=(125+1)/2=63.
On the other hand, a(3)=20 is even, so a(4)=5*20/2=50.

Mathematica

a[1] = 6; a[n_] := a[n] = If[ EvenQ[ a[n - 1]], 5*a[n - 1]/2, (a[n - 1] + 1)/2]; Table[ a[n], {n, 1, 50}]
NestList[If[EvenQ[#], (5#)/2, (#+1)/2]&, 6, 50] (* Harvey P. Dale, Nov 08 2012 *)

Prog

(PARI) s=6; for(n=1, 100, t=s; if(s%2==0, s=5*s/2, s=(s+1)/2); print1(t, ", "))
(Haskell)
a070870 n = a070870_list !! (n-1)
a070870_list = 6 : f 6 where
   f x = y : f y where
     y = (if even x then 5 * x else x + 1) `div` 2
-- Reinhard Zumkeller, Aug 15 2012

Crossrefs

Sequence in context: A205149 A289722 A351369 * A202749 A123623 A240990

Adjacent sequences: A070867 A070868 A070869 * A070871 A070872 A070873

Keyword

nonn,easy,nice

Author

N. J. A. Sloane, May 19 2002

Extensions

More terms from Benoit Cloitre and Robert G. Wilson v, May 20 2002

Example and extra link from Ben Branman, Jan 22 2012

Status

approved