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

Author

N. J. A. Sloane, Jan 12 2007

Keywords

• base
• easy
• nonn

Comments

Inspired by Angelini's sequence A114308.

Examples

			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.
		

Links

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

Crossrefs

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

Extensions

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