Voozh

A167456

Smallest sequence which lists the position of digits "6" in the sequence.

2, 6, 7, 8, 9, 66, 660, 700, 701, 702, 703, 704, 705, 707, 708, 709, 710, 711, 712, 713, 714, 715, 717, 718, 719, 760, 770, 771, 772, 773, 774, 775, 777, 778, 779, 780, 781, 782, 783, 784, 785, 787, 788, 789, 790, 791, 792, 793, 794, 795, 797, 798, 799, 800

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

The lexicographically earliest sequence such that a(1),a(2),a(3),... is the (increasing) list of the positions of digits "6" in the string obtained by concatenating all these terms, written in base 10.

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

We cannot have a(1)=1 (since then there's no "6" in the first place), but a(1)=2 is possible.

Then a(2) must start with a digit "6", so a(2)=6 is the smallest possible choice.

This allows us to go on with a(3)=7, a(4)=8, a(5)=9, but then must be follow 4 digits "6" (the 6th through 9th digit of the sequence), so a(6)=66 and a(7)=660 are the smallest possible choices.

Then the reasoning continues in analogy with A167452-A167455.

PROG

(PARI) concat([ [2, 6, 7, 8, 9, 66, 660], vector((66-9)\3-1, i, 700-(i<=6)+i+(i>=16)), [760], select(x->x%10-6 & x\10%10-6, vector((660-66)\3+10, i, 770+i-1)) ])

CROSSREFS

Cf. A098645, A167519, A167520, A167452 - A167455.

Sequence in context: A250183 A260139 A118471 * A023633 A332938 A037310

Adjacent sequences: A167453 A167454 A167455 * A167457 A167458 A167459

KEYWORD

base,nonn

AUTHOR

M. F. Hasler, Nov 19 2009

STATUS

approved

URL: https://oeis.org/A167456

⇱ A167456 - OEIS