A039636 Number of steps to fixed point of "n -> n/2 or (n-1)/2 until result is prime".

1, 1, 1, 2, 1, 2, 1, 3, 3, 2, 1, 3, 1, 2, 2, 4, 1, 4, 1, 3, 3, 2, 1, 4, 4, 2, 2, 3, 1, 3, 1, 5, 5, 2, 2, 5, 1, 2, 2, 4, 1, 4, 1, 3, 3, 2, 1, 5, 5, 5, 5, 3, 1, 3, 3, 4, 4, 2, 1, 4, 1, 2, 2, 6, 6, 6, 1, 3, 3, 3, 1, 6, 1, 2, 2, 3, 3, 3, 1, 5, 5, 2, 1, 5, 5, 2, 2, 4, 1, 4, 4, 3, 3, 2, 2, 6, 1, 6, 6, 6, 1, 6

Offset: 1

Author

Wouter Meeussen

Keywords

• nonn

Links

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

Crossrefs

Cf. A039634-A039645.

Cf. A010051, A039634, A039637, A039642, A039643.

Programs

Haskell

a039636 1 = 1
a039636 n = snd $ until ((== 1) . a010051 . fst)
                        (\(x, i) -> (x `div` 2 , i + 1)) (n, 1)
-- Reinhard Zumkeller, Nov 17 2013

Mathematica

nerlist[ n_Integer ] := Length/@Drop[ FixedPointList[ If[ EvenQ[ # ]&&#>2, #/ 2, If[ PrimeQ[ # ]||(#===1), #, (#-1)/2 ] ]&, n, 20 ], -1 ]

Extensions

Offset corrected by Reinhard Zumkeller, Nov 17 2013