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

1, 15, 2, 17, 37, 3, 19, 39, 59, 4, 21, 41, 61, 81, 5, 23, 43, 63, 83, 103, 6, 25, 45, 65, 85, 105, 125, 7, 27, 47, 67, 87, 107, 127, 147, 8, 9, 29, 49, 69, 89, 109, 129, 149, 169, 10, 195, 12, 13, 14, 33, 1, 16, 53, 18, 73, 20, 93, 22, 113, 24, 133, 26, 153

Offset

1,2

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Example

.  1   5    10   15   20   25   30   35   40   45   50   55   60
.  ....v....x....v....x....v....x....v....x....v....x....v....x....
.  12345678910111213141516171819202122232425262728293031323334353...
.  |||           | | |                 | |
.  |||           | | |                 | |
.  |||           | | |                 | +---  A116700(8) = 42
.  |||           | | |                 |          -> a(8) = 39
.  |||           | | |                 |
.  |||           | | |                 +--- A116700(5) = 32
.  |||           | | |                         -> a(5) = 37
.  |||           | | |
.  |||           | | + --- A116700(7) = 41  -> a(7) = 19
.  |||           | |
.  |||           | +--- A116700(4) = 31  -> a(4) = 17
.  |||           |
.  |||           +--- A116700(2) = 21  -> a(2) = 15
.  |||
.  ||+--- A116700(6) = 34  -> a(6) = 3
.  ||
.  |+--- A116700(3) = 23  -> a(3) = 2
.  |
.  +--- A116700(1) = 12  -> a(1) = 1, see also A007908.

Prog

(Haskell)
import Data.List (isPrefixOf, find)
import Data.Maybe (fromJust)
a220376 n = a220376_list !! (n-1)
a220376_list = at 1 where
   at z | (reverse (show (z - 1)) `isPrefixOf` fst bird) = at (z + 1)
        | otherwise                = (length $ fst bird) : at (z + 1)
        where bird = fromJust $ find ((show z `isPrefixOf`) . snd) xys
   xys = iterate (\(us, v : vs) -> (v : us, vs))
                 ([], concatMap show [0 ..])

Crossrefs

Cf. A117804.

Sequence in context: A040223 A272724 A076595 * A040224 A237649 A370371

Adjacent sequences: A220373 A220374 A220375 * A220377 A220378 A220379

Keyword

nonn,base,look

Author

Reinhard Zumkeller, Dec 13 2012

Status

approved