A030142 Odd numbers in which parity of digits alternates.

1, 3, 5, 7, 9, 21, 23, 25, 27, 29, 41, 43, 45, 47, 49, 61, 63, 65, 67, 69, 81, 83, 85, 87, 89, 101, 103, 105, 107, 109, 121, 123, 125, 127, 129, 141, 143, 145, 147, 149, 161, 163, 165, 167, 169, 181, 183, 185, 187, 189, 301, 303, 305, 307, 309, 321, 323

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base
• easy

Comments

a(n) = A179085(n) for n <= 25. - Reinhard Zumkeller, Jun 28 2010

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Index entries for 10-automatic sequences.

Crossrefs

Cf. A030143, A062285, intersection of A005408 and A030141.

Programs

Haskell

a030142 n = a030142_list !! (n-1)
a030142_list = filter odd a030141_list
-- Reinhard Zumkeller, Aug 31 2013

Mathematica

id[n_]:=IntegerDigits[n];t={}; Do[If[Length[id[n]]==1, AppendTo[t,n], If[Union[Abs[Differences[Boole /@ EvenQ[id[n]]]]] == {1}, AppendTo[t,n]]], {n,1,323,2}]; t (* Jayanta Basu, May 07 2013 *)
Join[{1, 3, 5, 7, 9}, Select[Range[21, 323, 2], Total[Abs[Differences[Mod[(id = IntegerDigits[#]), 2]]]] == Length[id] - 1 &]] (* Zak Seidov, May 07 2013 *)

Formula

(a(n) mod 2) * A228710(a(n)) = 1. - Reinhard Zumkeller, Aug 31 2013

Extensions

Offset corrected by Reinhard Zumkeller, Jun 28 2010