A238704 a(1)=1; the sequence S is always extended with the smallest integer not yet present in S that has the same parity as the first digit of the previous term.

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 2, 4, 6, 8, 10, 23, 12, 25, 14, 27, 16, 29, 18, 31, 33, 35, 37, 39, 41, 20, 22, 24, 26, 28, 30, 43, 32, 45, 34, 47, 36, 49, 38, 51, 53, 55, 57, 59, 61, 40, 42, 44, 46, 48, 50, 63, 52, 65, 54, 67, 56, 69, 58, 71, 73, 75, 77, 79, 81, 60, 62, 64, 66, 68, 70, 83, 72, 85, 74, 87, 76, 89, 78, 91, 93, 95, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125

Offset

1,2

Comments

This is a permutation of the natural numbers > 0.

Links

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

Eric Angelini, Parity given by first digit of the previous term

E. Angelini, Parity given by first digit of the previous term [Cached copy, with permission]

Index entries for sequences that are permutations of the natural numbers

Prog

(Haskell)
import Data.List (delete)
a238704 n = a238704_list !! (n-1)
a238704_list = 1 : f 1 [2..] where
   f x zs = g zs where
     g (y:ys) =
       if y `mod` 2 /= m then g ys else y : f y (delete y zs)
     m = a000030 x `mod` 2
-- Reinhard Zumkeller, Mar 03 2014

Crossrefs

Cf. A000030, A238718 (inverse).

Sequence in context: A329835 A356929 A187349 * A338742 A251238 A059547

Adjacent sequences: A238701 A238702 A238703 * A238705 A238706 A238707

Keyword

nonn,base,look

Author

Eric Angelini, Mar 03 2014

Status

approved