A125132 Self-describing sequence: sequence starts with a(1) = 1 and a(n) is chosen to be the smallest positive number not already in the sequence such that the assertion "sequence gives the positions of the odd digits when the sequence is read as a string of digits" is true.

1, 3, 5, 2, 7, 8, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 110, 10, 12, 14, 16, 111, 28, 30, 32, 34, 36, 48, 50, 52

Offset

1,2

Comments

Inspired by Angelini's sequence A114308.

Links

Jean-Marc Falcoz, Table of n, a(n) for n = 1..2001

Example

Here are the digits strung together (the odd digits occur at positions that are indexed by terms of the sequence):
-135278911
1315171921
2325272931
3335373941...
Explanation: a(2)=2? No. a(2)=3? Yes, but then the third term has to be odd and 2 has to appear later. a(3)=2? No, a(3) must be odd, so 5. a(4)? Now we can fill in the 2 that has been waiting. And so on.

Crossrefs

Cf. A125133 (missing numbers), A114308 (same except need a(n) > a(n-1)).

Sequence in context: A338872 A274421 A079313 * A352849 A243352 A026184

Adjacent sequences: A125129 A125130 A125131 * A125133 A125134 A125135

Keyword

base,easy,nonn

Author

N. J. A. Sloane, Jan 12 2007

Extensions

Corrected and extended by D. S. McNeil, Oct 22 2011

Status

approved