A338741 When a(n) is odd, a(n) is the number of odd digits present so far in the sequence, a(n) included.

0, 1, 2, 4, 6, 8, 10, 3, 12, 5, 14, 7, 16, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 28, 30, 32, 21, 34, 23, 36, 25, 38, 27, 40, 42, 44, 46, 48, 50, 29, 31, 33, 35, 37, 39, 52, 41, 54, 43, 56, 45, 58, 47, 60, 62, 64, 66, 68, 70, 49, 51, 53, 55, 57, 59, 72, 61, 74, 63, 76, 65, 78, 67, 80, 82, 84, 86, 88, 90, 69

Offset

1,3

Comments

The even nonnegative integers are present in their natural order. Some odd natural integers will never appear (19 for instance).

Links

Table of n, a(n) for n=1..80.

Example

The first odd term is a(2) = 1 and there is indeed 1 odd digit so far in the sequence (1 itself);
The next odd term is a(8) = 3 and there are now 3 odd digits so far (1, 1 and 3);
The next odd term is a(10) = 5 and there are now 5 odd digits so far (1, 1, 3, 1 and 5);
...
The next odd term is a(18) = 17 and there are indeed 17 odd digits so far in the sequence (1, 1, 3, 1, 5, 1, 7, 1, 9, 1, 1, 1, 3, 1, 5, 1, 7); etc.

Mathematica

Block[{a = {0}, c = 0}, Do[Block[{k = 1, s}, While[If[OddQ[k], Nand[FreeQ[a, k], k == c + Set[s, Total@ DigitCount[k, 10, {1, 3, 5, 7, 9}]]], ! FreeQ[a, k]], k++]; If[OddQ[k], c += s, c += Total@ DigitCount[k, 10, {1, 3, 5, 7, 9}]]; AppendTo[a, k]], {i, 79}]; a] (* Michael De Vlieger, Nov 06 2020 *)

Crossrefs

Cf. A338742, A338743, A338744, A338745, A338746 (variants on the same idea), A196564.

Sequence in context: A372144 A357379 A083167 * A115950 A077127 A082191

Adjacent sequences: A338738 A338739 A338740 * A338742 A338743 A338744

Keyword

base,nonn

Author

Eric Angelini and Carole Dubois, Nov 06 2020

Status

approved