A338744 When a(n) is even, a(n) is the number of odd digits present so far in the sequence, a(n) included.

0, 1, 3, 2, 5, 7, 4, 9, 11, 13, 10, 15, 17, 19, 21, 18, 23, 25, 20, 27, 29, 22, 31, 24, 33, 26, 35, 28, 37, 39, 41, 34, 43, 36, 45, 38, 47, 49, 40, 51, 42, 53, 44, 55, 46, 57, 48, 59, 61, 52, 63, 54, 65, 56, 67, 58, 69, 71, 73, 75, 77, 79, 70, 81, 72, 83, 74, 85, 76, 87, 78, 89, 91, 93, 95, 97, 99, 90, 101

Offset

1,3

Comments

The odd nonnegative integers are present in their natural order. Some even natural integers will never appear (6 for instance).

Links

Table of n, a(n) for n=1..79.

Example

The first even term is a(1) = 0 and there is indeed 0 odd digit so far in the sequence;
The next even term is a(4) = 2 and there are now 2 odd digits so far (1 and 3);
The next even term is a(7) = 4 and there are now 4 odd digits so far (1, 3, 5 and 7);
...
The even term a(11) = 10 and there are indeed 10 odd digits in the sequence so far (1, 3, 5, 7, 9, 1, 1, 1, 3 and 1); etc.

Mathematica

Block[{a = {0}, c = 0}, Do[Block[{k = 1, s}, While[If[EvenQ[k], Nand[FreeQ[a, k], k == c + Set[s, Total@ DigitCount[k, 10, {1, 3, 5, 7, 9}]]], ! FreeQ[a, k]], k++]; If[EvenQ[k], c += s, c += Total@ DigitCount[k, 10, {1, 3, 5, 7, 9}]]; AppendTo[a, k]], {i, 78}]; a] (* Michael De Vlieger, Nov 06 2020 *)

Crossrefs

Cf. A338741, A338742, A338743, A338745, A338746 (variants on the same idea), A196564.

Sequence in context: A276684 A105353 A115966 * A338745 A203602 A249559

Adjacent sequences: A338741 A338742 A338743 * A338745 A338746 A338747

Keyword

base,nonn

Author

Eric Angelini and Carole Dubois, Nov 06 2020

Status

approved