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 A220376 a(n) = position of first occurrence of n-th "early bird" number (cf. A116700) in the string 1234567891011121314151617181920212223242526272... . 2

%I

%S 1,15,2,17,37,3,19,39,59,4,21,41,61,81,5,23,43,63,83,103,6,25,45,65,

%T 85,105,125,7,27,47,67,87,107,127,147,8,9,29,49,69,89,109,129,149,169,

%U 10,195,12,13,14,33,1,16,53,18,73,20,93,22,113,24,133,26,153

%N a(n) = position of first occurrence of n-th "early bird" number (cf. A116700) in the string 1234567891011121314151617181920212223242526272... .

%H Reinhard Zumkeller, <a href="/A220376/b220376.txt">Table of n, a(n) for n = 1..10000</a>

%e . 1 5 10 15 20 25 30 35 40 45 50 55 60

%e . ....v....x....v....x....v....x....v....x....v....x....v....x....

%e . 12345678910111213141516171819202122232425262728293031323334353...

%e . ||| | | | | |

%e . ||| | | | | |

%e . ||| | | | | +--- A116700(8) = 42

%e . ||| | | | | -> a(8) = 39

%e . ||| | | | |

%e . ||| | | | +--- A116700(5) = 32

%e . ||| | | | -> a(5) = 37

%e . ||| | | |

%e . ||| | | + --- A116700(7) = 41 -> a(7) = 19

%e . ||| | |

%e . ||| | +--- A116700(4) = 31 -> a(4) = 17

%e . ||| |

%e . ||| +--- A116700(2) = 21 -> a(2) = 15

%e . |||

%e . ||+--- A116700(6) = 34 -> a(6) = 3

%e . ||

%e . |+--- A116700(3) = 23 -> a(3) = 2

%e . |

%e . +--- A116700(1) = 12 -> a(1) = 1, see also A007908.

%o import Data.List (isPrefixOf, find)

%o import Data.Maybe (fromJust)

%o a220376 n = a220376_list !! (n-1)

%o a220376_list = at 1 where

%o at z | (reverse (show (z - 1)) `isPrefixOf` fst bird) = at (z + 1)

%o | otherwise = (length \$ fst bird) : at (z + 1)

%o where bird = fromJust \$ find ((show z `isPrefixOf`) . snd) xys

%o xys = iterate (\(us, v : vs) -> (v : us, vs))

%o ([], concatMap show [0 ..])

%Y Cf. A117804.

%K nonn,base,look

%O 1,2

%A _Reinhard Zumkeller_, Dec 13 2012

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Last modified December 2 10:24 EST 2021. Contains 349437 sequences. (Running on oeis4.)