A258188 Smallest multiple of 7 not appearing earlier that ends with n.

21, 42, 63, 14, 35, 56, 7, 28, 49, 210, 511, 112, 413, 714, 315, 616, 217, 518, 119, 420, 721, 322, 623, 224, 525, 126, 427, 728, 329, 630, 231, 532, 133, 434, 735, 336, 637, 238, 539, 140, 441, 742, 343, 644, 245, 546, 147, 448, 749, 350, 651, 252, 553, 154

Offset

1,1

Comments

a(10*n) = 10*a(n).

The sequence is a permutation of the positive multiples of 7. - Vladimir Shevelev, May 24 2015

A258329(n) = a(n) / 7 is a permutation of the positive integers. - Reinhard Zumkeller, May 27 2015

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..9999

Mathematica

a[n_] := a[n] = For[k = 7, True, k = k + 7, If[Divisible[k - n, 10^IntegerLength[n]] && FreeQ[Array[a, n-1], k], Return[k]]]; Array[a, 54] (* Jean-François Alcover, Feb 07 2018 *)

Prog

(Haskell)
import Data.List (isPrefixOf, delete)
a258188 n = a258188_list !! (n-1)
a258188_list = f 1 $ tail $ zip
   a008589_list $ map (reverse . show) a008589_list where
   f x ws = g ws where
     g ((u, vs) : uvs) = if isPrefixOf xs vs
                         then u : f (x + 1) (delete (u, vs) ws) else g uvs
     xs = reverse $ show x

Crossrefs

Cf. A008589, A258083, A258217, A258329.

Sequence in context: A260749 A040420 A192130 * A037978 A089059 A114384

Adjacent sequences: A258185 A258186 A258187 * A258189 A258190 A258191

Keyword

nonn,base

Author

Eric Angelini and Reinhard Zumkeller, May 23 2015

Status

approved